Sheet transport device, image reading device, image forming device

Abstract

This can suppress the decrease in accuracy of detecting sheet skew. [Solution] The system includes a sensor unit having a first sensor for detecting a sheet and a second sensor for detecting a sheet at a position different from the first sensor in the width direction, and a control unit capable of performing a re-feeding process, which re-executes the feeding operation by the transport unit if a sheet to be transported by the transport unit is not detected within a set time based on the detection result of the sensor unit. The control unit stops the transport operation by the transport unit for sheets on which the re-feeding process has not been performed if a first elapsed time has elapsed since the sheet was detected by the first sensor but the sheet is not detected by the second sensor, and does not stop the transport operation by the transport unit for sheets on which the re-feeding process has been performed a set number of times, even if a first elapsed time has elapsed since the sheet was detected by the first sensor but the sheet is not detected by the second sensor (S130; YES).

Description

Technical Field

[0001] The present invention relates to a sheet conveying device, an image reading device, and an image forming device for conveying a sheet.

Background Art

[0002] A document conveying device such as an automatic document feeder (hereinafter referred to as ADF) provided in an image reading device mounted on a copying machine, a facsimile device, or the like has become widespread. In a sheet conveying device mounted on such a document conveying device, a technique for detecting the inclination of the leading end of a conveyed sheet (hereinafter referred to as skew detection) using a plurality of sheet detection sensors provided in a conveying unit is known. This technique arranges a plurality of sheet detection sensors at different positions in the sheet width direction on the conveying path, and detects the skew occurring in the sheet from the difference in the timing when each sensor detects the conveyed sheet.

[0003] For example, in an ADF, when a stack of documents (documents of different widths mixed and loaded) having different lengths in the width direction (hereinafter referred to as the main scanning direction) orthogonal to the sheet conveying direction is loaded, the side regulating plate of the tray is fixed in accordance with the sheet having the largest length in the main scanning direction. Therefore, a smaller sheet than that is conveyed in a state where skew is likely to occur. Therefore, a technique has been developed to reduce the possibility of false detection of skew by increasing the determination threshold value of skew detection when a setting of documents of different widths mixed and loaded is made (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the sheet conveying device described in Patent Document 1 mentioned above, if the sheet conveying speed becomes slower than expected due to wear of the conveying rollers or adhesion of paper dust, the timing of detection by the sheet detection sensor becomes larger. As a result, the amount of sheet skew may be overestimated, and even if the actual amount of skew is below the threshold for stopping conveying, it may be mistakenly judged as exceeding the threshold, leading to a problem of reduced accuracy in detecting sheet skew.

[0006] The present invention aims to provide a sheet transport device, an image reading device, and an image forming device that can suppress the decrease in accuracy of sheet skew detection. [Means for solving the problem]

[0007] One aspect of the present invention is a sheet conveying device comprising: a loading section on which sheets are loaded; a conveying section that performs a sheet conveying operation including a feeding operation for separating and feeding the sheets loaded in the loading section one by one; a sensor section having a first sensor for detecting sheets being conveyed by the conveying section and a second sensor for detecting sheets at a position different from the first sensor in the width direction perpendicular to the sheet conveying direction; and a control unit that, based on the detection result of the sensor section, can execute a re-feeding process to re-execute the feeding operation by the conveying section if a sheet being conveyed by the conveying section is not detected within a set time, wherein the control unit stops the conveying operation by the conveying section for sheets on which the re-feeding process has not been executed if a first elapsed time has elapsed since the sheet was detected by the first sensor but the sheet is not detected by the second sensor, and does not stop the conveying operation by the conveying section for sheets on which the re-feeding process has been executed a set number of times, even if a first elapsed time has elapsed since the sheet was detected by the first sensor but the sheet is not detected by the second sensor.

[0008] Another aspect of the present invention is an image reading device characterized by comprising the sheet transport device described above and an image reading unit for reading an image formed on a sheet.

[0009] Another aspect of the present invention is an image forming apparatus characterized by comprising the image reading device described above and an image forming unit that forms an image on a sheet. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress the decrease in accuracy of detecting sheet skew in a sheet transport device, an image reading device, and an image forming device. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view of the image forming apparatus according to the first embodiment, as seen from the front. [Figure 2] This is a cross-sectional view of the image reading device according to the first embodiment, as seen from the front. [Figure 3] This is a control block diagram of an image reading device according to the first embodiment. [Figure 4] This figure shows the case when a bound sheet is fed by the image reading device according to the first embodiment, where (a) is a cross-sectional view from the front when the amount of obliqueness is small, (b) is a plan view thereof, (c) is a cross-sectional view from the front when the amount of obliqueness is large, and (d) is a plan view thereof. [Figure 5] This figure shows the case when a sheet is fed by the image reading device according to the first embodiment, where (a) is a front view cross-sectional view when a sheet is detected by one sheet detection sensor, and (b) is a plan view thereof. (c) is a front view cross-sectional view when a sheet is detected by two sheet detection sensors, and (d) is a plan view thereof. (e) is a front view cross-sectional view when the smallest size sheet is detected, and (f) is a plan view thereof. [Figure 6] This is the screen displayed in the operation unit according to the first embodiment when transport is stopped due to diagonal movement detection. [Figure 7] This is the first half of a flowchart showing the processing procedure when reading a sheet using the image reading device according to the first embodiment. [Figure 8] This is the latter half of the flowchart showing the processing procedure when reading a sheet using the image reading device according to the first embodiment. [Figure 9] The first half of a flowchart showing the processing procedure when reading a sheet by the image reading apparatus according to the second embodiment. [Figure 10] The second half of a flowchart showing the processing procedure when reading a sheet by the image reading apparatus according to the second embodiment. [Figure 11] The first half of a flowchart showing the processing procedure when reading a sheet by the image reading apparatus according to the third embodiment. [Figure 12] The second half of a flowchart showing the processing procedure when reading a sheet by the image reading apparatus according to the third embodiment. [Figure 13] The first half of a flowchart showing the processing procedure when reading a sheet by the image reading apparatus according to the fourth embodiment. [[ID=!15]] [Figure 14] The second half of a flowchart showing the processing procedure when reading a sheet by the image reading apparatus according to the fourth embodiment. [Figure 15] A flowchart showing the procedure of the slant detection execution determination process by the user according to the fourth embodiment. [Figure 16] A screen displayed when the conveyance is stopped by slant detection in the operation unit according to the fourth embodiment. [Figure 17] The first half of a flowchart showing the processing procedure when reading a sheet by the image reading apparatus according to the reference example. [Figure 18] The second half of a flowchart showing the processing procedure when reading a sheet by the image reading apparatus according to the reference example.

Embodiments for Carrying Out the Invention

[0012] <00!0093><The First Embodiment> Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIGS. 1 to 8. In this embodiment, as an example of the image forming apparatus 1, a case where an electrophotographic monochrome printer is applied will be described. However, the present invention is not limited to the image forming apparatus 1 of an electrophotographic monochrome printer, and it may be full-color, and further, it may be applied to a tandem type or an inkjet recording type image forming apparatus.

[0013] [Image forming apparatus]<00​​​​​​​​The sheet S, placed on the manual feed tray 37e by the user, is fed into the main body 1A of the device by the feed roller 38 and transported to the registration roller pair 36. The registration roller pair 36 stops the leading edge of the sheet S to correct its skew and resumes transporting the sheet S in accordance with the progress of the image formation operation, which is the toner image formation process by the image forming unit 33.

[0016] The image forming unit 33 forms an image on the sheet S based on the image information read by the image reading device 5. The image forming unit 33 is an electrophotographic unit equipped with a photosensitive drum 21, which is a photoreceptor. The photosensitive drum 21 is rotatable along the transport direction of the sheet S, and a charger 18, exposure device 23, developer 24, transfer charger 25, separation charger 26, and cleaner 27 are arranged around the photosensitive drum 21. The charger 18 uniformly charges the surface of the photosensitive drum 21. The exposure device 23 exposes the photosensitive drum 21 based on image information input from the image reading device 5, etc., and forms an electrostatic latent image on the photosensitive drum 21.

[0017] The developer unit 24 contains a two-component developer including toner and carrier, and develops the electrostatic latent image into a toner image by supplying charged toner to the photosensitive drum 21. The toner image supported on the photosensitive drum 21 is transferred to the sheet S transported from the registration roller pair 36 by the bias electric field formed by the transfer charger 25. The sheet S, onto which the toner image has been transferred, is separated from the photosensitive drum 21 by the bias electric field formed by the separation charger 26 and transported toward the fixer unit 29 by the pre-fixer transport unit 28. Any remaining toner or other deposits on the photosensitive drum 21 that were not transferred to the sheet S are removed by the cleaner 27, and the photosensitive drum 21 prepares for the next image formation operation.

[0018] The sheet S, transported to the fixing unit 29, is held between a pair of rollers, heated, and pressurized, and the image is fixed by the melting and solidification of toner. If image output is complete, the sheet S with the fixed image is discharged via the discharge roller pair 10 to the discharge tray 30 which protrudes to the outside of the main body 1A of the device. In double-sided printing, when an image is formed on the back side of the sheet S, the sheet S that has passed through the fixing unit 29 is reversed by the reversal unit 39, and transported to the registration roller pair 36 by the double-sided transport unit 40. Then, the sheet S, with the image formed again by the image forming unit 33, is discharged to the discharge tray 30. The image forming unit 33 described above is just one example of an image forming unit; for example, an inkjet type image forming unit or an offset printing type printing mechanism may be used as the image forming unit.

[0019] [Image reading device] The image reading device 5, positioned above the main body 1A of the image forming apparatus 1, comprises a scanner unit 100 and an ADF 200 (Auto Document Feeder), and optically scans the original document to read image information. The image information, converted into an electrical signal by the image reading device 5, is transferred to the control unit 160 located in the main body 1A via the controller 500 (see Figure 3). As a result, the image forming apparatus 1 forms an image on the recording medium based on the image information read by the image reading device 5.

[0020] Figure 2 is a cross-sectional view showing an example of the image reading device 5 of this embodiment. The scanner unit 100 includes a surface reading unit 101, a white reference member 108, a document glass 109, a reading movement guide 110, a timing belt 151, a document motor 169, etc. The scanner unit 100 drives the document motor 169 and moves the surface reading unit 101 along the reading movement guide 110 via the timing belt 151, reading the surface of the document placed on the document glass 109 one line at a time to read an image.

[0021] The surface reading unit 101 is an example of an image reading unit, and reads the image formed on the sheet transported by the feeding unit 7. For example, a contact image sensor (CIS) can be used as the surface reading unit 101. The surface reading glass 106 reads the image of the document that has been transported onto the surface reading glass 106 by the ADF 200 using the surface reading unit 101.

[0022] The ADF200 includes a feeding unit 7, which is an example of a sheet transport device, a pair of registration rollers 215, a back-side reading unit 230, and an output tray 225. The feeding unit 7 includes a document tray 201, which is an example of a stacking unit for stacking a stack of one or more documents, a guide width regulating plate 202, a width detection sensor 205, a transport unit 240, and a sensor unit 241. The transport unit 240 has a separation roller 211 and a pickup roller 210, and performs a sheet transport operation that includes a feeding operation to separate and feed the sheets stacked on the document tray 201 one by one, and transports them in the transport direction.

[0023] The guide width regulating plate 202 is installed on the document tray 201 and swings in the width direction (main scanning direction) perpendicular to the document transport direction to restrict the movement of the document in the main scanning direction. The width detection sensor 205 acquires width information in accordance with the swing of the guide width regulating plate 202. The separation roller 211 and the pickup roller 210 are separation mechanisms that separate documents one by one and prevent the stack of documents from protruding from the document tray 201 and moving downstream before the start of document transport. By dropping the pickup roller 210 onto the top surface of the stack of documents loaded on the document tray 201 and rotating it, the document on the top of the stack is transported. The document transported by the pickup roller 210 is separated and transported one at a time by the action of the separation roller 211. This separation is achieved by known separation technology.

[0024] When the document separated by the separation roller 211 turns on the separation sensor 212, a timer count begins. This count is used to calculate the detection start timing of the double-feed detection sensor 213 and to calculate the document length. Subsequently, when the document reaches the vicinity of the double-feed detection sensor 213, double-feed detection begins. The document is then transported via the registration sensor 214 to the registration roller pair 215, where it is brought into contact with the nip position of the registration roller pair 215. The leading edge of the document is formed into a loop shape, thereby eliminating skew during document transport.

[0025] Downstream of the separation sensor 212 in the transport direction, a first sheet detection sensor 228a, which is an example of a first sensor, and a second sheet detection sensor 228b, which is an example of a second sensor, are arranged. The first sheet detection sensor 228a detects the sheets being transported by the transport unit 240. The second sheet detection sensor 228b detects the sheets being transported by the transport unit 240 at a different position from the first sheet detection sensor 228a in the width direction perpendicular to the sheet transport direction. The first sheet detection sensor 228a and the second sheet detection sensor 228b detect the oblique angle of the leading edge of the original document on the top of the stack of original documents separated and fed from the original document tray 201 by the transport unit 240.

[0026] In this embodiment, the separation sensor 212 is an example of a third sensor and an upstream sensor, and detects the sheet being transported by the transport unit 240 at a position different from that of the first sheet detection sensor 228a and the second sheet detection sensor 228b in the transport direction. Furthermore, a pull-out sensor 227 is positioned downstream of the first sheet detection sensor 228a and the second sheet detection sensor 228b in the transport direction. The pull-out sensor 227 is an example of a downstream sensor, and is located downstream of the separation sensor 212 in the transport direction. Both the separation sensor 212 and the pull-out sensor 227 are different sensors from the first sheet detection sensor 228a and the second sheet detection sensor 228b. The sensor unit 241 has a plurality of sensors, including the first sheet detection sensor 228a and the second sheet detection sensor 228b, and for example, it has the separation sensor 212 and the pull-out sensor 227.

[0027] Downstream of the registration roller pair 215, a transport path is arranged to transport the document that has passed through the registration roller pair 215 toward the front-side reading glass 106. When the document sent to the transport path turns on the lead sensor 216, this triggers a timer 171 (shown in Figure 3, described later) to set a timer for when the leading edge of the document reaches the front-side document reading position 107. In the case of simultaneous double-sided reading, a timer is also set for when the leading edge of the document reaches the back-side document reading position 220. After that, the document is transported to the front-side document reading position 107 by the lead roller pair 217.

[0028] When the timer 171 expires for surface reading, surface reading begins. Specifically, the document passing over the surface reading glass 106 is illuminated from below the surface glass by the surface LED 102 in the surface reading unit 101. The surface image of the document is read by the surface line sensor 103 through the surface lens array 104 by this reflected light. While reading the surface of the document, it is transported from the surface document reading position 107 to the back document reading position 220 by the lead roller pair 219.

[0029] When the timer 171 expires for back-side reading, back-side reading begins. In the case of double-sided reading, as the document passes over the back-side white opposing member, which is integrated with the back-side reading glass 234, it is illuminated by the back-side LED 231 in the back-side reading unit 230. The back-side image of the document is read by the back-side line sensor 232, which is a CIS, by reading the reflected light through the back-side lens array 233. After passing the back-side document reading position 220, the document is transported to the lead roller pair 221 and then discharged onto the discharge tray 225 by the discharge roller pair 223.

[0030] In this embodiment, the case in which CIS is applied as the front reading unit 101 and the back reading unit 230 has been described, but it is not limited to this. For example, a CCD configured with a reduction optical system using mirrors can also be used.

[0031] [Control System] Figure 3 is a block diagram showing the control system of the image reading device 5 in this embodiment. The image reading device 5 includes a CPU 164, which is a central processing unit, a ROM 165, which is read-only memory, and a RAM 166, which is random access memory. The ROM 165 stores a control program for realizing document reading, and the RAM 166 stores input data and working data.

[0032] The lighting control unit 167 controls the on / off switching of the LEDs 102 and 231. The scanning control unit 168 controls the drive of the document feeder motor 169. The document feeder motor 169 is connected to the surface reading unit 101 by a timing belt 151, etc., and when the document feeder motor 169 is driven, the surface reading unit 101 can slide in the sub-scanning direction on the reading movement guide 110. Similarly, the scanning control unit 168 controls the drive of the document transport motor 170 built into the ADF 200. The document transport motor 170 is connected to the separation roller 211, registration roller pair 215, lead roller pair 217, lead roller pair 219, lead roller pair 221, ejection roller pair 223, etc. When the document transport motor 170 is driven, these rollers rotate and the document is transported to the transport path in the ADF 200.

[0033] The front line sensor 103 is built into the front reading unit 101 and receives light reflected from the document when illuminated by the front LED 102. This is input to the A / D conversion unit 161, where the analog data is converted to digital data. The image processing unit 162 performs image processing to generate image data. Similarly, the back line sensor 232 is built into the back reading unit 230 and receives light reflected from the document when illuminated by the back LED 231. The subsequent processing is the same as on the front side, so the explanation is omitted. The document size acquisition unit 163 acquires the scanned document size information input by the operation unit 506 of the controller 500 (described later), or acquires document size information based on a combination of the states of the width detection sensor 205 and the length detection sensor 206.

[0034] The shading RAM 254 consists of arithmetic memory 255 and coefficient memory 256, and is accessible by read and write operations from the CPU 164. The non-volatile memory 257 is a memory that retains values ​​even when the power to the image reading device 5 is turned off. For example, it is used to store shading target values ​​when performing shading correction with the shading correction circuit 253, or alarm and error information that occurs during a job.

[0035] Timer 171 receives and counts pulse signals emitted at predetermined distances as the document transport motor 170 is driven, and when it reaches a preset count value, it sends a timer completion signal to the CPU 164. This makes it possible to measure the distance the document has advanced. Surface image reading control unit 172 performs image reading processing. When the timer value set in Timer 171 is reached and the CPU 164 receives the signal, it is sent as a trigger signal to the surface image reading control unit 172 and the back image reading control unit 173. Based on this trigger, the surface image reading control unit 172 and the back image reading control unit 173 start acquiring the document image.

[0036] The transport sensor detection unit 174 acquires the on / off state of each sensor installed in the document transport path. When the leading edge of the document reaches each sensor or the trailing edge of the document leaves each sensor, a signal is transmitted to the transport sensor detection unit 174. The CPU 164 receives this signal as an interrupt, enabling it to transmit processing to the timer 171 and other components without delay. The first sheet detection sensor 228a and the second sheet detection sensor 228b detect the oblique angle of the leading edge of the document on the top of the stack of documents separated and fed from the document tray 201.

[0037] The controller 500 converts the original image read by the image reader 5 into a format that can be output to the sheet S set in the image forming apparatus 1. Alternatively, the controller 500 can convert the image into a format that can be output to a PC, and also handles user operations and overall device management. The image reader 5 and the controller 500 are connected by a communication line 180, and various data signals are sent and received between the image reader 5 and the controller 500 via the communication line 180. The controller 500 is equipped with a central processing unit CPU 501, read-only memory ROM 502, and random access memory RAM 503. ROM 502 stores control programs for image conversion and overall device management, while RAM 503 stores input data and work data.

[0038] The image processing unit 504 performs processing to convert the original document image read by the image reading device 5 into a format that can be output by the image forming apparatus 1. The image memory 505 temporarily stores this image data. The operation unit 506 consists of a touch panel equipped with a screen and operation buttons, and accepts button operations from the user as well as outputting various information to the user on the screen.

[0039] In this embodiment, the image reading device 5 and the controller 500 are configured to have a CPU, ROM, and RAM, respectively. However, for example, the image reading device 5 may not have a CPU, etc., and may share the CPU, ROM, and RAM of the controller 500. In that case, the communication line 180 does not exist, and other control units connected to the CPU 164 are directly connected to the CPU 501. In this embodiment, the configuration is described with each CPU present, but configurations in which they are shared can be implemented by appropriately modifying the description.

[0040] [Feed Retry] The image reading device 5 is equipped with a feed jam (sheet jam) detection function. The control unit 160 determines that a feed jam has occurred when, even after sheet transport is started by driving the document transport motor 170, the sheet is not transported within a predetermined time from the detection start position to a predetermined sensor located downstream of the transport path. In other words, there are cases where the sheet does not reach the predetermined sensor due to delays in sheet transport caused by wear of the pickup roller 210 or adhesion of paper dust, or when multiple sheets stacked together stick together and cannot be separated smoothly. The control unit 160 determines that a feed jam has occurred in such cases. In this embodiment, the control unit 160 detects a feed jam in the section from when the leading edge of the sheet reaches the separation sensor 212 until it reaches the extraction sensor 227.

[0041] On the other hand, if the sheet is not transported to the predetermined sensor even after the sheet transport is started by driving the document transport motor 170, there is a feed retry process as a means of remedy. In the feed retry process of this embodiment, if it is determined that a feed jam has occurred, the document transport motor 170 is stopped, and then the pickup roller 210 is raised by driving a motor other than the document transport motor 170. After that, the pickup roller 210 is lowered and the document transport motor 170 is driven. Through this process, even if the sheet does not reach the predetermined sensor, the feed process can be repeated, thereby preventing the occurrence of a feed jam.

[0042] [Skewing detection] Generally, the ADF200 cannot separate and feed / transport so-called "bound sheets," such as stapled or glued sheets. Such sheets are at risk of being damaged by the separation operation performed by the separation roller 211 and separation pad 226. In the case of sheets with one end bound in the width direction, the separation operation causes skewing at the leading edge of the first sheet, followed by damage to the sheet. Therefore, in this embodiment, the first sheet detection sensor 228a and the second sheet detection sensor 228b provided in the feeding and transport section of the ADF200 detect skewing in the sheet and stop the feeding and transport process at that point to prevent damage to the sheet.

[0043] Figures 4(a) to 4(d) are explanatory diagrams showing a portion of the ADF200 when attempting to feed and transport a sheet with one end in the sheet width direction bound. Figures 4(a) and 4(c) are cross-sectional views of the ADF200, and Figures 4(b) and 4(d) are plan views showing the transport path of the ADF200 laid out in a plane. The dashed lines between Figure 4(a) and Figure 4(b), and between Figure 4(c) and Figure 4(d), indicate the correspondence of the positions of each sensor, roller, etc. in the two figures, respectively. Similarly, Figures 5(a) to 5(f) are explanatory diagrams showing a portion of the ADF200 when attempting to feed and transport a normal sheet in an inclined state. Figures 5(a), 5(c), and 5(e) are cross-sectional views of the ADF200, and Figures 5(b), 5(d), and 5(f) are plan views showing the transport path of the ADF200 laid out in a plane. The dashed lines between Figure 5(a) and Figure 5(b), between Figure 5(c) and Figure 5(d), and between Figure 5(e) and Figure 5(f) indicate the correspondence between the positions of each sensor, roller, etc., in the two figures, respectively.

[0044] The sheet detection sensor acquisition unit 228 (see Figure 3) is connected to a first sheet detection sensor 228a and a second sheet detection sensor 228b. The first sheet detection sensor 228a and the second sheet detection sensor 228b are sensors for detecting the leading edge of the sheet, and are composed of, for example, photosensors. As shown in Figure 4(b), the first sheet detection sensor 228a and the second sheet detection sensor 228b are arranged side by side with a gap in the sheet width direction, with the separation roller 211 in between. Due to this arrangement, in the case of a normal sheet (a sheet that is not a bound sheet) and no skewing occurs, the first sheet detection sensor 228a and the second sheet detection sensor 228b detect the leading edge of the sheet almost simultaneously.

[0045] In the case of bound sheets, if the leading edge of the first sheet becomes skewed due to the separation operation, one sensor will first detect the leading edge of the sheet, but then the bound sheet bundle cannot be transported downstream from the separation roller 211, and the other sensor will not detect the leading edge of the sheet. In the example in Figure 4, as shown in Figure 4(b), the second sheet detection sensor 228b detects the leading edge of the sheet. As the feeding and transport of the sheets progresses, as shown in Figure 4(d), the skew of the first sheet becomes greater due to the separation operation, but the first sheet detection sensor 228a still does not detect the leading edge of the sheet. If the feeding and transport continues in this state, there is a risk of sheet damage.

[0046] On the other hand, in the case of a normal sheet where skew is occurring, there is a time lag between one sensor detecting the leading edge of the sheet and the other sensor detecting the leading edge of the sheet. In the example in Figure 5, as shown in Figure 5(b), the second sheet detection sensor 228b detects the leading edge of the sheet. As the sheet is fed and transported, as shown in Figure 5(d), the first sheet detection sensor 228a detects the leading edge of the sheet.

[0047] As shown in Figures 4 and 5, the approximate amount of skew occurring in the sheet can be calculated from the elapsed time since one sensor detected the leading edge of the sheet. Let V [mm / s] be the sheet transport speed, and W [mm] be the distance in the width direction between the first sheet detection sensor 228a and the second sheet detection sensor 228b. Let t [s] be the elapsed time from when one sensor detects the leading edge of the sheet until the other sensor detects the leading edge of the sheet, and let θ0 be the amount of skew occurring in the sheet. In this case, the following equation 1 holds true. t = W × tanθ 0 ÷ V ... (Equation 1)

[0048] In this embodiment, if the sheet S is skewed by 3° or more, there is a risk of sheet damage occurring due to the separation operation of the binding sheet, and the sheet transport process is stopped and the document transport motor 170 is stopped. That is, in this case, equation 2 is derived as the relational expression. tθ = W × tanθ ÷ V ... (Equation 2)

[0049] In Equation 2, if the other sheet detection sensor does not detect the leading edge of the sheet within 3° of time t after one sheet detection sensor detects the leading edge of the sheet, it is determined that a skew of 3° or more has occurred, and the transport process is stopped. In other words, the system is designed to make this determination even if only one of the first sheet detection sensor 228a or the second sheet detection sensor 228b detects the sheet.

[0050] As shown in Figure 4(d), when a bound sheet is fed and transported, the skew that occurs at the leading edge of the sheet is characterized by a small amount of skew near the end on the side with the binding and a large amount of skew near the other end. Therefore, when detecting bound sheets by skew detection, it is desirable to place the sensor used for skew detection close to the edge in the width direction of the sheet. By placing the sensor used for skew detection close to the edge in the width direction of the sheet, it is possible to detect skew that occurs at the leading edge of the bound sheet on the side without the binding, regardless of whether the binding is on the far side or the near side in the width direction.

[0051] In this embodiment, as shown in Figures 5(e) and 5(f), the first sheet detection sensor 228a and the second sheet detection sensor 228b are positioned near the edge in the width direction of the sheet when the smallest size sheet is fed and transported. This makes it possible to detect the skew even when the smallest size sheet that can be transported by the ADF200 has a 3° skew.

[0052] As mentioned above, while skew detection helps prevent damage to the binding sheets, the system determines whether a sheet is binding or not based on the detection time difference between the sheet detection sensors at both ends. Therefore, the sheet feeding and transport process may be stopped even for documents other than binding sheets. For example, when placing a stack of documents on the document tray 201, if one end of the documents is not aligned and they are placed in a rough set, the situation shown in Figures 5(a) and (b) will occur, and since it is impossible to distinguish them from binding sheets, the sheet feeding and transport process will be stopped.

[0053] Furthermore, if the sheet transport speed becomes slower than expected due to wear of the pickup roller 210 or adhesion of paper dust, the difference in detection timing between the first sheet detection sensor 228a and the second sheet detection sensor 228b becomes large. In this case, the amount of sheet skew may be overestimated, and even if the actual amount of skew is below the threshold for stopping transport, it may be mistakenly judged as exceeding that threshold.

[0054] [Display on the control panel when diagonal movement is detected] Figure 6 shows an example of the display content shown on the operation unit 506 when the sheet detection sensor acquisition unit 228 determines that the transported document is skewed. This screen is displayed on the operation unit 506 at the same time that the sheet feeding and transport process is stopped. When it is determined that the document is skewed, the text is displayed in a way that guides the user to take the next steps by listing the possible causes of the stoppage as described above. If the transported document is actually a bound sheet, the user presses the stop button 506b to stop the job itself, and removes the document remaining in the transport path in the ADF 200 that contains the bound sheet. Then, the user either removes the bound sheet or removes the staples or other binding medium, places the stack of documents back on the document tray 201, and restarts the job.

[0055] If the documents actually transported are not bound sheets and are of the same width, it is possible that the documents were placed at an angle when placed on the document tray 201, or that the documents are prone to skew due to wrinkles or creases. If it is a rough set where one end of the sheets is not aligned, then at least one side of the sheet stack should be aligned and then placed on the document tray 201 again. However, if the sheets are prone to skew, transporting them again may cause the sheet detection sensor acquisition unit 228 to detect skew again, potentially interrupting the transport. Since the sheets cannot be read in this state, to enable this, in this case, the button 506a to temporarily turn off skew detection is pressed. When this is pressed, information to that effect is stored in the RAM 503. When sheet transport is performed in this state, the information from RAM 503 is transmitted to the CPU 164 via the communication line 180, and the sheet detection sensor acquisition unit 228 will not perform detection during sheet transport, or even if it does, it will not calculate or judge the amount of skew. Therefore, the job will not be interrupted, and the aforementioned sheet bundle can be read.

[0056] In this case, the document transport speed may become slower than expected due to wear of the transport section 240, such as the pickup roller 210, or the accumulation of paper dust. In this case, the difference in detection timing between the first sheet detection sensor 228a and the second sheet detection sensor 228b becomes large, leading to an overestimation of the sheet's skew. In this case, even if the actual skew is below the threshold for stopping transport, it may be mistakenly judged as being above it. Therefore, in this embodiment, the threshold is changed based on the actual sheet speed. The control flow for changing the threshold in this embodiment will be described in detail below.

[0057] [Control Flow] Next, the control flow in the image reading device 5's scrolling job will be explained using Figures 7 and 8. Figures 7 and 8 are flowcharts of the control process in this embodiment, from receiving a request to start scrolling to reading the original image and transmitting it to the controller 500. In this embodiment, the control unit 160 will be described in the case where it performs a re-feeding process to re-execute the feeding operation if the sheet is not transported to the extraction sensor 227 even after the sheet has been transported a predetermined distance by the document transport motor 170. The processes shown in Figures 7 and 8 are performed by the CPU 164 of the control unit 160 executing a program stored in the ROM 165.

[0058] When the control unit 160 starts processing a skimming job, it starts transporting the sheets (S101). The control unit 160 determines whether the sheet has reached the separation sensor 212 (S102). If the control unit 160 determines that the sheet has not reached the separation sensor 212 (S102; NO), it makes the determination again (S102). If the control unit 160 determines that the sheet has reached the separation sensor 212 (S102; YES), it determines whether the sheet has reached the first sheet detection sensor 228a and the second sheet detection sensor 228b (S103). If the control unit 160 determines that the sheet has not reached the first sheet detection sensor 228a and the second sheet detection sensor 228b (S103; NO), it makes the determination again (S103).

[0059] If the control unit 160 determines that the sheet has reached the first sheet detection sensor 228a and the second sheet detection sensor 228b (S103; YES), it determines whether the sheet has reached the pull-out sensor 227 (S104). At this point, the sheet's skew amount θ can be calculated, but until the decision on whether to refeed the sheet is complete, the control unit does not determine whether to stop the sheet's transport using the skew amount.

[0060] If the control unit 160 determines that the sheet has reached the pull-out sensor 227 (S104; YES), it determines whether or not to perform skew detection (S105). If the control unit 160 determines that skew detection should be performed (S105; YES), it performs skew detection and calculates the amount of skew θ of the sheet (S106).

[0061] The control unit 160 determines whether the amount of skew θ exceeds the threshold T (S107). The threshold T is set in advance to an amount of skew that makes it difficult to read the sheet correctly, and in this embodiment, T = 3°. If the control unit 160 determines that the amount of skew θ exceeds the threshold T (S107; YES), it stops the sheet transport by the transport unit 240 because there is a risk of sheet damage (S134). Subsequently, the control unit 160 notifies the controller 500 of the occurrence of a feed jam due to skew (S135) and terminates the job.

[0062] In this embodiment, the control unit 160 detects skew if a sheet is not detected by the other sheet detection sensor even after a first elapsed time has elapsed since a sheet was detected by one of the first sheet detection sensors 228a and 228b. A second elapsed time shorter than the first elapsed time is also defined. In this case, the control unit 160 does not detect skew if a sheet is not detected by the other sheet detection sensor even after a second elapsed time has elapsed since a sheet was detected by one of the first sheet detection sensors 228a and 228b. That is, if the time difference in the detection timing of the first sheet detection sensor 228a and 228b is greater than or equal to a threshold, skew is detected; if it is less than the threshold, skew is not detected.

[0063] The control unit 160 is capable of performing a refeeding process. If the control unit 160 detects skew in a sheet for which a refeeding process has not been performed, it performs a transport stop process to stop the sheet transport operation. In this embodiment, the execution of the transport stop process means a series of processes from detecting skew (S106), determining that the amount of skew θ exceeds the threshold T (S107; YES), to stopping the transport (S134). That is, if the control unit 160 detects skew in a sheet for which a refeeding process has not been performed, it stops the transport operation by the transport unit 240.

[0064] On the other hand, in this embodiment, the control unit 160 refrains from performing the transport stop process depending on whether the refeeding process has been performed a set number of times. In this embodiment, the set number of times is 1, but this may be set to multiple times. Also, in this embodiment, not performing the transport stop process means not performing skew detection (S106), or even if skew is detected, not determining whether the amount of skew θ exceeds the threshold T, or even if it is determined, not performing (S134). In other words, the control unit 160 does not stop the transport operation by the transport unit 240 even if skew is detected for a sheet for which the refeeding process has been performed a set number of times.

[0065] If the control unit 160 determines that the amount of skew θ does not exceed the threshold T (S107; NO), it considers that the sheet is being fed normally. If the control unit 160 determines that the amount of skew θ does not exceed the threshold T (S107; NO), or if it determines in S105 not to perform skew detection, it waits for the sheet to reach the reading start position (S108). If the control unit 160 determines that the sheet has not reached the reading start position (S108; NO), it waits again (S108). If the control unit 160 determines that the reading position has been reached (S108; YES), it performs image reading processing (S109). Here, the control unit 160 stores the image data in memory. After reading the image, the control unit 160 performs correction by image processing as necessary and then sends the image to the controller 500 (S110). When the transfer of one image is complete, the reading process for one sheet is completed.

[0066] The control unit 160 determines whether the transfer of all images has been completed (S111). If the control unit 160 determines that the transfer of all images has not been completed (S111; NO), it makes the determination again (S111). If the control unit 160 determines that the transfer of all images has been completed (S111; YES), it determines whether there is another sheet on the document tray 201 (S112). If the control unit 160 determines that there is another sheet on the document tray 201 (S112; YES), it starts feeding the next sheet (S101). If the control unit 160 determines that there is no sheet on the document tray 201 (S112; NO), it determines that the reading process for all sheets has been completed, so it stops feeding after the last sheet has been transported (S113) and terminates the job.

[0067] On the other hand, if the control unit 160 determines that the sheet has not reached the pull-out sensor 227 (S104; NO), it determines whether the sheet has been transported a predetermined distance from the point of arrival at the separation sensor 212 (S130). In this embodiment, the predetermined distance is 50 mm, which is the distance of 35 mm in the transport path between the separation sensor 212 and the pull-out sensor 227 plus a jam detection margin of 15 mm. If the control unit 160 determines that the sheet has been transported a predetermined distance from the point of arrival at the separation sensor 212 (S130; YES), it determines that an abnormality has occurred in the transport of the sheet and determines whether the number of refeeding operations C is less than the threshold R (S131). Here, the control unit 160 determines whether the number of refeeding operations C performed so far is less than a predetermined threshold R. The threshold R is the maximum number of times refeeding operations are performed, and in this embodiment, R = 3.

[0068] If the control unit 160 determines that the number of refeeding operations C is less than the threshold R (S131; YES), it performs a refeeding operation (feeding retry) and adds 1 to the number of refeeding operations C (S132). In this embodiment, the refeeding operation involves stopping the document transport motor 170, raising the pickup roller 210, then lowering the pickup roller 210, and driving the document transport motor 170. Note that the retry of the feeding operation is not limited to that described in this embodiment.

[0069] In this embodiment, the control unit 160 determines whether or not an abnormality has occurred in the sheet transport based on whether or not the sheet has been transported a predetermined distance from the separation sensor 212. However, it is not limited to this, and the control unit 160 may, for example, determine that an abnormality has occurred in the sheet transport if the sheet being transported by the transport unit 240 is not detected within a set time. The control unit 160 executes a re-feeding process if the sheet being transported by the transport unit 240 is not detected by the pull-out sensor 227 within a set time from the time it is detected by the separation sensor 212.

[0070] The control unit 160 determines that the sheet transport is not proceeding normally after the refeeding process and sets the skew detection process to stop (S133). This is because the decision to perform the refeeding process indicates that the sheet transport is slower than expected. In this case, when detecting the tilt of the leading edge of the sheet, there is a possibility that the time difference between when one of the first sheet detection sensor 228a and the second sheet detection sensor 228b detects the sheet and when the other detects it will be large. Since the amount of skew of the sheet is calculated from this time difference, in the above case, there is a possibility that a larger amount of skew will be calculated than the actual amount of skew. Therefore, even if the actual amount of skew is below the threshold for stopping transport, there is a possibility of misjudging it as being above the threshold, so the skew detection process is stopped if the refeeding process has been performed even once.

[0071] If the control unit 160 sets the skew detection process to stop, or determines that the sheet has not been transported a predetermined distance since reaching the separation sensor 212 (S130; NO), it determines whether the sheet has reached the pull-out sensor 227 again (S104). Also, if the control unit 160 determines that the number of re-feeding operations C is not less than the threshold R (S131; NO), it stops the transport of the sheet by the transport unit 240 because there is a risk of sheet damage (S134). After that, the control unit 160 notifies the controller 500 of the occurrence of a feed jam due to skew (S135) and terminates the job.

[0072] As described above, according to the image forming apparatus 1 of this embodiment, the control unit 160 does not perform skew detection processing on sheets that have undergone refeeding processing, does not perform transport stop processing, and does not stop the sheet (S105). As a result, even if the transport speed of the original document becomes slower than expected due to wear of the transport unit 240 or adhesion of paper dust, false detection of the amount of skew θ can be suppressed and the decision to stop the sheet can be made with high accuracy.

[0073] In particular, in this embodiment, the decision to refeed is made by the pull-out sensor 227 located downstream of the first sheet detection sensor 228a and the second sheet detection sensor 228b. Specifically, the control unit 160 executes a transport stop process if the sheet being transported by the transport unit 240 is detected by the pull-out sensor 227 within a set time from the time the sheet being detected by the separation sensor 212 is detected. Also, if the sheet being transported by the transport unit 240 is not detected by the pull-out sensor 227 within a set time from the time the sheet being detected by the separation sensor 212 is detected, the control unit 160 executes a refeed process without executing a transport stop process. As a result, even if the sheet is detected by the first sheet detection sensor 228a and the second sheet detection sensor 228b before the pull-out sensor 227, the skew processing can be temporarily suspended and the decision to refeed can be made first.

[0074] <Second Embodiment> Next, a second embodiment of the present invention will be described in detail with reference to Figures 9 and 10. In this embodiment, the control unit 160 differs from the first embodiment in that, after the start of sheet feeding, if the sheet is not transported to the separation sensor 212 even after the document transport motor 170 has transported the sheet a predetermined distance, it performs a re-feeding process. However, the other components are the same as in the first embodiment, so the same reference numerals are used and detailed descriptions are omitted.

[0075] [Control Flow] The control flow in the image reading device 5's skimming job in this embodiment will be explained using Figures 9 and 10. Figures 7 and 8 are flowcharts of the control process in this embodiment, from receiving a skimming start request to reading the document image and transmitting it to the controller 500. The processes shown in Figures 9 and 10 are carried out by the CPU 164 of the control unit 160 executing a program stored in the ROM 165.

[0076] When the control unit 160 starts processing a read-through job, it starts transporting the sheet (S201). The control unit 160 determines whether the sheet has reached the separation sensor 212 (S202). If the control unit 160 determines that the sheet has not reached the separation sensor 212 (S202; NO), it determines whether the sheet has been transported a predetermined distance from the start of feeding (S230). In this embodiment, the predetermined distance is 45 mm, which is the distance of 30 mm from the start position of feeding to the separation sensor 212 plus a jam detection margin of 15 mm. Here, the processing from S230 to S233 is the same as the processing from S130 to S133 shown in Figure 7, so the explanation is omitted.

[0077] In this embodiment, the control unit 160 executes a re-feeding process if the sheet being transported by the transport unit 240 is not detected by the separation sensor 212 within a set time from the start of the feeding operation.

[0078] On the other hand, if the control unit 160 determines that the sheet has reached the separation sensor 212 (S202; YES), it determines whether the sheet has reached the first sheet detection sensor 228a and the second sheet detection sensor 228b (S203). If the control unit 160 determines that the sheet has not reached the first sheet detection sensor 228a and the second sheet detection sensor 228b (S203; NO), it makes the determination again (S203).

[0079] If the control unit 160 determines that the sheet has reached the first sheet detection sensor 228a and the second sheet detection sensor 228b (S203; YES), it determines whether or not the sheet has reached the pull-out sensor 227 (S204). If the control unit 160 determines that the sheet has not reached the pull-out sensor 227 (S204; NO), it makes the determination again (S204). If the control unit 160 determines that the sheet has reached the pull-out sensor 227 (S204; YES), it determines whether or not to perform skew detection (S205). Here, the processes in S205 to S213 and S234 to S235 are the same as the processes in S105 to S113 and S134 to S135 shown in Figure 8, so their explanation is omitted.

[0080] As described above, in the image forming apparatus 1 of this embodiment, the control unit 160 does not perform skew detection processing on sheets that have undergone refeeding processing, does not execute transport stop processing, and does not stop the sheets (S205). As a result, even if the transport speed of the original document becomes slower than expected due to wear of the transport unit 240 or adhesion of paper dust, false detection of the amount of skew θ can be suppressed and the decision to stop the sheets can be made with high accuracy.

[0081] Furthermore, according to this embodiment, the control unit 160 executes a re-feeding process if the sheet being transported by the transport unit 240 is not detected by the separation sensor 212 within a set time from the start of the feeding operation. Therefore, since it is not necessary to use the detection result of the pull-out sensor 227, the control can be simplified.

[0082] <Third Embodiment> Next, a third embodiment of the present invention will be described in detail with reference to Figures 11 and 12. In this embodiment, the control unit 160 differs in configuration from the first embodiment in that it corrects the skew detection threshold when refeeding processing is performed. However, the other configurations are the same as in the first embodiment, so the same reference numerals are used and detailed descriptions are omitted.

[0083] [Control Flow] The control flow in the image reading device 5 in this embodiment will be explained using Figures 11 and 12. Figures 11 and 12 are flowcharts of the control process from receiving a request to start the scan in this embodiment to reading the document image and transmitting it to the controller 500. The processes shown in Figures 11 and 12 are carried out by the CPU 164 of the control unit 160 executing a program stored in the ROM 165.

[0084] The processes in S301-S306 and S330-S332 are the same as the processes in S101-S106 and S130-S132 shown in Figures 7 and 8, so their explanation is omitted. In S332, the control unit 160 performs a refeeding process (feeding retry), adds 1 to the number of refeeding processes C, and then determines that the sheet transport is not proceeding normally because a refeeding process has been performed, and sets the correction value A for the skew detection threshold (S333). The correction value A for the skew detection threshold is a correction value that increases the skew detection threshold, and in this embodiment, A=2. The decision to perform a refeeding process indicates that the sheet transport is slower than expected. In this case, when detecting the tilt of the leading edge of the sheet, there is a possibility that the time difference between when one of the first sheet detection sensor 228a and the second sheet detection sensor 228b detects the sheet and when the other detects it will become large. Because the amount of sheet skew is calculated from this time difference, in the above case, there is a possibility that a larger amount of skew may be calculated than the actual amount of skew. Therefore, even if the actual amount of skew is below the threshold for stopping transport, there is a possibility that it may be mistakenly judged as being above it. For this reason, when re-feeding is performed, the threshold for detecting skew is corrected to be larger. After that, the control unit 160 determines whether the sheet has reached the pull-out sensor 227 again (S304).

[0085] In other words, in this embodiment, the control unit 160 detects skewness in sheets for which refeeding processing has not been performed if a sheet is not detected by the other sheet detection sensor 228a or 228b even after a first elapsed time has elapsed since the sheet was detected by one of the sheet detection sensors 228a or 228b. In response to the execution of refeeding processing, the control unit 160 executes a transport stop process if a sheet is not detected even after a third elapsed time, which is longer than the first elapsed time, has elapsed since the sheet was detected by one of the sheet detection sensors 228a or 228b.

[0086] Meanwhile, in S306, the control unit 160 performs skew detection and calculates the amount of skew θ of the sheet, then determines whether the amount of skew θ exceeds the product of the threshold T and the correction value A (S307). The threshold T here is set in advance to an amount of skew that is considered difficult to read the sheet normally, and in this embodiment, T = 3°. If the control unit 160 determines that the amount of skew θ exceeds the product of the threshold T and the correction value A (S307; YES), there is a risk of sheet damage, so it stops the conveying of the sheet by the conveying unit 240 (S334). After that, the control unit 160 notifies the controller 500 of the occurrence of a feeding jam due to skew (S335) and terminates the job.

[0087] If the control unit 160 determines that the amount of skew θ does not exceed the threshold T (S307; NO), it considers that the sheet is being fed normally. The processing in S308 to S313 is the same as the processing in S108 to S113 shown in Figure 7, so the explanation is omitted.

[0088] As described above, in the image forming apparatus 1 of this embodiment, the control unit 160 does not perform skew detection processing on sheets that have undergone refeeding processing, does not execute transport stop processing, and does not stop the sheets (S305). As a result, even if the transport speed of the original document becomes slower than expected due to wear of the transport unit 240 or adhesion of paper dust, false detection of the amount of skew θ can be suppressed and the decision to stop the sheets can be made with high accuracy.

[0089] <Fourth Embodiment> Next, a fourth embodiment of the present invention will be described in detail with reference to Figures 13 to 15. In this embodiment, the control unit 160 differs in configuration from the first embodiment in that the user can select to stop the skew detection process during the refeeding process. However, the other configurations are the same as in the first embodiment, so the same reference numerals are used and detailed descriptions are omitted.

[0090] [Control Flow] Figures 13, 14, and 15 will be used to explain the control flow in the image reading device 5 in this embodiment for a scrolling job. Figures 13 to 15 are flowcharts of the control process in this embodiment, from receiving a request to start scrolling to reading the original image and transmitting it to the controller 500. The processes shown in Figures 13 to 15 are carried out by the CPU 164 of the control unit 160 executing a program stored in the ROM 165.

[0091] The processes in S501 to S513 and S530 to S531 are the same as the processes in S101 to S113 and S130 to S131 shown in Figures 7 and 8, so their explanation is omitted. If the control unit 160 determines that the number of refeeding processes C is less than the threshold R (S531; YES), it prompts the user to decide whether or not to perform skew detection (S532).

[0092] Here, the processing procedure for determining whether to perform skew detection will be explained using Figure 15. The control unit 160 stops the transport of the sheet (S601) and displays a notification on the operation unit 506 warning that skew detection cannot be performed normally, as shown in Figure 16 (S602). Figure 16 is an example of what is displayed on the operation unit 506 when it is determined that feeding is not being performed normally, and it is displayed on the operation unit 506 immediately after the sheet feeding and transport process is stopped.

[0093] The control unit 160 determines whether the user will perform skew detection (S603). The decision to perform refeeding indicates that the sheet transport is slower than expected. In this case, when detecting the tilt of the leading edge of the sheet, there is a possibility that the time difference between when one of the first sheet detection sensor 228a and the second sheet detection sensor 228b detects the sheet and when the other detects it will be large. Since the amount of sheet skew is calculated from this time difference, in the above case, there is a possibility that a larger amount of skew will be calculated than the actual amount of skew.

[0094] Therefore, even if the actual amount of skew is below the threshold for stopping transport, there is a possibility of a misjudgment that it is above it. To address this, a warning is displayed to the user, allowing them to choose whether or not to stop the skew detection process. If the user decides to perform skew detection and presses the restart button 560b (S603; YES), the second mode is executed, and the process for deciding whether or not to perform skew detection is terminated. If the user decides not to perform skew detection and presses the button 560a to temporarily turn off skew detection (S603; NO), the first mode is executed, and the system is set not to perform skew detection for this job (S630).

[0095] Thus, the control unit 160 can select between a first mode in which the transport stop process is not performed for a sheet that has undergone the re-feeding process once, and a second mode in which the transport stop process is performed.

[0096] As described above, in the image forming apparatus 1 of this embodiment, the control unit 160 does not perform skew detection processing for sheets that have undergone refeeding processing, does not execute transport stop processing, and does not stop the sheet (S505). As a result, even if the transport speed of the original document becomes slower than expected due to wear of the transport unit 240 or adhesion of paper dust, false detection of the amount of skew θ can be suppressed and the decision to stop the sheet can be made with high accuracy.

[0097] According to this embodiment, for sheets that have undergone refeeding processing, it is possible to select between a first mode in which the transport stop processing is not performed and a second mode in which the transport stop processing is performed. Therefore, the user can make the appropriate selection according to the actual sheets and work content.

[0098] In each of the embodiments described above, if the user decides not to perform skew detection, the decision is made valid for that job and reset for the next job. However, this is not the only option; even in the next job, skew detection may be disabled until the user sets it to resume.

[0099] Furthermore, in the embodiments described above, the control unit 160 is configured to allow selection of whether or not to perform the transport stop process in the first mode and the second mode, but it is not limited to this. For example, as in the third embodiment, it may be possible to select between a third mode and a fourth mode, which select the setting of the correction value A of the skew detection threshold. A third elapsed time longer than the first elapsed time is defined. The third mode here is a mode in which, for a sheet that has undergone refeeding processing, the transport stop process is performed if the sheet is not detected by the other sensor even after the third elapsed time has elapsed since the sheet was detected by one of the sheet detection sensors 228a and 228b. The fourth mode is a mode in which the transport stop process is performed when the first elapsed time has elapsed since the sheet was detected by one of the sheet detection sensors 228a and 228b.

[0100] <Reference example> Next, a reference example of the present invention will be described in detail with reference to Figures 17 and 18. In this embodiment, the control unit 160 differs in configuration from the first embodiment in that it can stop the skew detection process without performing refeeding. However, the other configurations are the same as in the first embodiment, so the same reference numerals are used and detailed descriptions are omitted.

[0101] [Control Flow] Figures 17 to 18 illustrate the control flow in the image reading device 5 in this embodiment for a scrolling job. Figures 17 to 18 are flowcharts of the control process from receiving a request to start scrolling in this embodiment to reading the document image and transmitting it to the controller 500. The processes shown in Figures 17 to 18 are carried out by the CPU 164 of the control unit 160 executing a program stored in the ROM 165.

[0102] The processing in S401 to S413 is the same as the processing in S101 to S113 shown in Figures 7 and 8, so the explanation is omitted. If the control unit 160 determines that the sheet has not reached the pull-out sensor 227 (S404; NO), it determines whether the sheet has been transported a predetermined distance from the point of arrival at the separation sensor 212 (S430). If the control unit 160 determines that the sheet has been transported a predetermined distance from the point of arrival at the separation sensor 212 (S430; YES), it determines that an abnormality has occurred in the sheet transport and sets the skew detection process to stop (S431). This indicates that if the sheet has been transported a predetermined distance but has not reached the pull-out sensor 227, the sheet transport is slower than expected. In this case, when detecting the inclination of the leading edge of the sheet, there is a possibility that the time difference between when one of the first sheet detection sensor 228a and the second sheet detection sensor 228b detects the sheet and when the other detects it will become large. Because the amount of sheet skew is calculated from this time difference, in the above case, there is a possibility that a larger amount of skew may be calculated than the actual amount of skew. Therefore, even if the actual amount of skew is below the threshold for stopping transport, there is a possibility that it may be mistakenly judged as being above it. For this reason, if the sheet has not reached the pull-out sensor 227 after being transported a predetermined distance, the skew detection process is stopped.

[0103] [Other embodiments] In each of the embodiments described above, a timeout is applied to determine whether to perform a refeeding process, which is the timeout from the start of the feeding operation until detection by the separation sensor 212, or from detection by the separation sensor 212 until detection by the withdrawal sensor 227. However, this is not the only case, and it can be applied in general when a sheet is detected by one of the multiple sensors provided in the sensor unit 241, but is not detected by any of the other sensors downstream within a set time. Alternatively, it may also apply when a sheet is not detected by any of the sensors in the sensor unit 241 within a set time after the control unit 160 commands the feeding operation.

[0104] In the embodiments described above, the sheet transport device was described in the case where it is applied to the feeding unit 7 of the image reading device 5, but it is not limited to this. The sheet transport device of the present invention can be applied to all sheet transport devices that transport sheets in the image reading device 5 and the image forming device 1. [Explanation of Symbols]

[0105] 1…Image forming apparatus, 5…Image reading apparatus, 7…Feeding unit (sheet transport device), 33…Image forming section, 101…Surface reading section (image reading section), 160…Control unit, 201…Document tray (loading section), 212…Separation sensor (third sensor, upstream sensor), 227…Pulling sensor (downstream sensor), 228a…First sheet detection sensor (first sensor), 228b…Second sheet detection sensor (second sensor), 240…Transport section, 241…Sensor section

Claims

1. The loading section where the sheets are loaded, A conveying unit that performs a sheet transport operation, including a feeding operation that separates and feeds the sheets loaded in the loading section one by one, A sensor unit having a first sensor for detecting a sheet being transported by the transport unit, and a second sensor for detecting a sheet at a position different from the first sensor in the width direction perpendicular to the sheet transport direction, The system includes a control unit capable of executing a re-feeding process, which re-executes the feeding operation by the transport unit if the sheet being transported by the transport unit is not detected within a set time based on the detection result of the sensor unit, The control unit, For sheets that have not undergone the refeeding process, if the second sensor does not detect the sheet even after a first elapsed time has elapsed since the first sensor detected the sheet, the transport operation by the transport unit is stopped. Even if the sheet is not detected by the second sensor after the first elapsed time has elapsed since the first sensor detected the sheet, the transport unit will not stop the transport operation for the sheet that has been subjected to the refeeding process a set number of times. A sheet conveying device characterized by the following features.

2. The control unit, with respect to a sheet for which the refeeding process has not been performed, will not stop the transport operation by the transport unit if the sheet is detected by the second sensor within a second elapsed time shorter than the first elapsed time after the sheet was detected by the first sensor. The sheet conveying device according to feature 1.

3. The control unit, For sheets that have not undergone the refeeding process, if the second sensor does not detect the sheet even after the first elapsed time has elapsed since the first sensor detected the sheet, the transport stop process is executed to stop the transport operation. Depending on whether the refeeding process has been executed the specified number of times, the transport stop process will not be executed. The sheet conveying device according to feature 1.

4. The control unit can select between a first mode in which the transport stop process is not performed for sheets for which the refeeding process has been performed the set number of times, and a second mode in which the transport stop process is performed. The sheet conveying device according to feature 3.

5. The control unit, For sheets that have not undergone the refeeding process, if the second sensor does not detect the sheet even after the first elapsed time has elapsed since the first sensor detected the sheet, the transport stop process is executed to stop the transport operation. If, after the refeeding process has been executed the set number of times, the second sensor does not detect the sheet even after a third elapsed time, which is longer than the first elapsed time, has elapsed since the first sensor detected the sheet, the transport stop process is executed. The sheet conveying device according to feature 1.

6. The control unit, for the sheet in which the refeeding process has been executed the set number of times, A third mode in which, if a sheet is not detected by the second sensor even after a third elapsed time, which is longer than the first elapsed time, has elapsed since the first sensor detected the sheet, the transport stop process is executed. A fourth mode in which the transport stop process is executed when the first elapsed time has elapsed since the sheet was detected by the first sensor, It is possible to select The sheet conveying device according to claim 5.

7. The sensor unit has a third sensor that detects the sheet being transported by the transport unit at a position different from the first and second sensors in the transport direction. The control unit executes the re-feeding process if the sheet being transported by the transport unit is not detected by the third sensor within the set time from the start of the feeding operation. The sheet conveying device according to feature 1.

8. The sensor unit has a plurality of sensors, including the first sensor and the second sensor. The plurality of sensors include an upstream sensor and a downstream sensor located downstream of the upstream sensor in the transport direction. The control unit executes the re-feeding process if the sheet being transported by the transport unit is not detected by the downstream sensor within the set time from the time it is detected by the upstream sensor. The sheet conveying device according to feature 1.

9. The upstream sensor and the downstream sensor are both different sensors from the first sensor and the second sensor. The sheet conveying device according to claim 8.

10. The downstream sensor is located downstream of the first sensor and the second sensor in the transport direction. The control unit, With respect to a sheet for which the refeeding process has not been performed, if the sheet is not detected by the second sensor even after the first elapsed time has elapsed since the sheet was detected by the first sensor, If the sheet being transported by the transport unit is detected by the downstream sensor within the set time from the time the upstream sensor detects it, a transport stop process is executed to stop the transport operation. If the sheet being transported by the transport unit is not detected by the downstream sensor within the set time from the time it is detected by the upstream sensor, the re-feeding process is executed without executing the transport stop process. The sheet conveying device according to feature 9.

11. A sheet conveying device according to any one of claims 1 to 10, It comprises an image reading unit that reads an image formed on a sheet, An image reading device characterized by the following.

12. The image reading device according to claim 11, It comprises an image forming unit that forms an image on a sheet, An image forming apparatus characterized by the following:

Images