Sheet conveying device, image reading device, and image forming device

Abstract

To provide a sheet conveying device, an image reading device, and an image forming device capable of suppressing a decrease in the accuracy of sheet skew detection.SOLUTION: A sheet conveying device comprises: a conveying unit for conveying a sheet; a sensor unit having a first sensor and a second sensor for detecting the sheet conveyed by the conveying unit; and a control unit capable of executing first stop processing (S130) for stopping the conveyance of the sheet by the conveying unit when one of the first sensor and the second sensor does not detect the sheet until a threshold time elapses after the other of the first sensor and the second sensor detects the sheet, and speed detection processing (S104) for measuring the speed of the sheet conveyed by the conveyance unit based on the detection result of the sensor unit. The control unit sets the threshold time to the first time when the speed of the sheet measured in the speed detection processing is the first speed, and sets the threshold time to the second time longer than the first time when the speed of the sheet measured in the speed detection processing is the second speed slower than the first speed (S107).SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Document transport devices, such as automatic document feeders (hereinafter referred to as ADFs) provided in image reading devices attached to copiers, facsimile machines, etc., are becoming widespread. A technology is known for sheet transport devices installed in such document transport devices, which uses multiple sheet detection sensors provided in the transport section to detect the skew of the leading edge of a sheet being transported (hereinafter referred to as skew detection). This technology involves arranging multiple sheet detection sensors at different positions in the sheet width direction on the transport path, and detecting the skew of the sheet from the difference in timing at which each sensor detects the sheet being transported.

[0003] For example, when a stack of documents (mixed document widths) with different lengths in the width direction (hereinafter referred to as the main scanning direction) perpendicular to the sheet conveyance direction is loaded in an ADF, the side regulating plates of the tray are fixed to match the sheet with the longest length in the main scanning direction. As a result, smaller sheets are conveyed in a state where they are more likely to skew. Therefore, a technology has been developed to reduce the possibility of erroneous detection of skew by increasing the judgment threshold for skew detection when a mixed document width setting is made (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-101900 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the sheet conveying device described in Patent Document 1, if the sheet conveying speed becomes slower than expected due to wear of the conveying roller, adhesion of paper dust, etc., the difference in detection timing of the sheet detection sensor becomes large. As a result, the amount of skew of the sheet is calculated to be larger, and even if the amount of skew is actually below the threshold for stopping conveyance, it may be erroneously determined to be above the threshold, resulting in a problem of reduced accuracy in detecting skew of the sheet.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet conveying device, an image reading device, and an image forming device that can suppress a decrease in accuracy in detecting skew of a sheet. [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 stacked; a conveying section that separates the sheets loaded on the loading section one by one and conveys them in a conveying direction; a sensor section having a first sensor that detects the sheets conveyed by the conveying section at a first detection position and a second sensor that detects the sheets at a second detection position that is different from the first detection position in a width direction perpendicular to the conveying direction; and a control unit capable of executing a first stop process that stops the conveying of the sheet by the conveying section if one of the first sensor and the second sensor does not detect the sheet within a threshold time after the other of the first sensor and the second sensor detects the sheet; and a speed detection process that measures the speed of the sheet conveyed by the conveying section based on the detection result of the sensor unit, wherein the control unit sets the threshold time to a first time when the sheet speed measured in the speed detection process is a first speed, and sets the threshold time to a second time that is longer than the first time when the sheet speed measured in the speed detection process is a second speed that is slower than the first speed.

[0008] Another aspect of the present invention is a sheet conveying device comprising: a loading section on which sheets are loaded; a conveying section that separates the sheets loaded on the loading section one by one and conveys them in a conveying direction; a sensor section having a first sensor that detects the sheets conveyed by the conveying section at a first detection position and a second sensor that detects the sheets at a second detection position that is different from the first detection position in a width direction perpendicular to the conveying direction; and a control unit capable of executing a first stop process that stops the conveying of the sheet by the conveying section in response to a detection result of detecting skew of the sheet based on the detection result of the sensor unit; and a speed detection process that measures the speed of the sheet conveyed by the conveying section based on the detection result of the sensor unit, wherein the control unit is capable of selectively executing a first mode in which the first stop process is executed when the measured sheet speed is slower than a threshold speed, and a second mode in which the first stop process is not executed.

[0009] Another aspect of the present invention is an image reading device comprising the above-mentioned sheet conveying device and an image reading unit that reads an image formed on a sheet conveyed by the sheet conveying device.

[0010] Another aspect of the present invention is an image forming apparatus comprising the above-mentioned image reading device and an image forming unit that forms an image on a sheet based on information of the image read by the image reading device. [Effects of the Invention]

[0011] According to the present invention, it is possible to suppress a decrease in the accuracy of detecting skew of a sheet in a sheet conveying device, an image reading device, and an image forming device. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view of an image forming apparatus according to an embodiment, as viewed from the front. [Figure 2] 1 is a cross-sectional view of an image reading apparatus according to an embodiment, as viewed from the front. [Figure 3] FIG. 2 is a control block diagram of the image reading apparatus according to the embodiment. [Figure 4] 10A and 10B are diagrams illustrating a case where a binding sheet is fed by an image reading device according to an embodiment, in which (a) is a cross-sectional view as viewed from the front when the amount of skew is small, (b) is a plan view thereof, (c) is a cross-sectional view as viewed from the front when the amount of skew is large, and (d) is a plan view thereof. [Figure 5] 1A and 1B are diagrams illustrating a case where a sheet is fed by an image reading device according to an embodiment, in which (a) is a cross-sectional view seen from the front when a sheet is detected by one sheet detection sensor, (b) is a plan view thereof, (c) is a cross-sectional view seen from the front when a sheet is detected by two sheet detection sensors, (d) is a plan view thereof, (e) is a cross-sectional view seen from the front when a minimum size sheet is detected, and (f) is a plan view thereof. [Figure 6] 10 is a screen displayed on the operation unit according to the embodiment when conveyance is stopped due to skew detection. [Figure 7] 10 is a flowchart illustrating a processing procedure for detecting skew based on conveyance efficiency in the image reading apparatus according to the embodiment. [Figure 8] 10 is a flowchart illustrating a processing procedure for calculating a transport efficiency in the image reading apparatus according to the embodiment. [Figure 9] 10 is a screen displayed on the operation unit according to the embodiment when transport is stopped due to a decrease in transport efficiency. [Figure 10] 10 is a flowchart showing a processing procedure for calculating an average conveying efficiency in the image reading apparatus according to the embodiment. [Figure 11] 10 is a flowchart showing a processing procedure for determining whether to resume skew detection in the image reading apparatus according to the embodiment. [Figure 12] 10 is a flowchart showing a processing procedure for determining whether skew is detected after calculation of transport efficiency in the image reading apparatus according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] First Embodiment A first embodiment of the present invention will be described in detail below with reference to Figures 1 to 9. In this embodiment, a case where an electrophotographic monochrome printer is applied as an example of the image forming apparatus 1 is described. However, the present invention is not limited to an electrophotographic monochrome printer image forming apparatus 1, and may also be applied to a full-color image forming apparatus, or even a tandem type or inkjet recording type image forming apparatus.

[0014] [Image forming equipment] The schematic configuration of an image forming apparatus 1 equipped with an image reading device 5 will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view of the image forming apparatus 1 according to this embodiment. In the following, the position where a user faces an operation unit (not shown) through which various inputs / settings are made to the image forming apparatus 1 will be defined as the "front side" of the image forming apparatus 1, and the rear side will be defined as the "rear side." In other words, Fig. 1 shows the internal configuration of the image forming apparatus 1 as seen from the front side.

[0015] The apparatus main body 1A has an image forming unit 33 that forms an image on a sheet S, which is a recording medium, and a sheet feeding unit 6 that feeds the sheet S to the image forming unit 33. The sheet feeding unit 6 has sheet storage units 37a, 37b, 37c, and 37d that can store sheets of different sizes. The sheets stored in the sheet storage units 37a, 37b, 37c, and 37d are fed out by pickup rollers 2a, 2b, 2c, and 2d. Then, the sheets are separated one by one by feed rollers 3a, 3b, 3c, and 3d and retard rollers 4a, 4b, 4c, and 4d and delivered to the corresponding conveyance roller pairs 31. The sheets S are then delivered in order to the multiple conveyance roller pairs 31 arranged along the sheet conveyance path, and are conveyed to the registration roller pair 36.

[0016] The sheet S placed on the manual feed tray 37e by the user is fed into the apparatus main body 1A by the feed roller 38 and conveyed to the registration roller pair 36. The registration roller pair 36 stops the leading edge of the sheet S to correct skew, and resumes conveyance of the sheet S in accordance with the progress of the image forming operation, which is the toner image forming process by the image forming unit 33.

[0017] The image forming unit 33 forms an image on the sheet S based on 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 photosensitive body. The photosensitive drum 21 is rotatable along the conveyance direction of the sheet S, and a charger 18, an exposure device 23, a developing device 24, a transfer charger 25, a separation charger 26, and a 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 to light based on image information input from the image reading device 5 or the like, and forms an electrostatic latent image on the photosensitive drum 21.

[0018] The developing device 24 contains a two-component developer containing 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 carried on the photosensitive drum 21 is transferred to a sheet S conveyed from a pair of registration rollers 36 by a bias electric field formed by a transfer charger 25. The sheet S with the transferred toner image is separated from the photosensitive drum 21 by a bias electric field formed by a separation charger 26, and is conveyed toward a fixing unit 29 by a pre-fixing conveying unit 28. Note that any deposits, such as transfer residual toner, remaining on the photosensitive drum 21 without being transferred to the sheet S are removed by a cleaner 27, and the photosensitive drum 21 is prepared for the next image forming operation.

[0019] The sheet S conveyed to the fixing unit 29 is sandwiched between a pair of rollers and heated and pressurized, and the image is fixed by melting and fixing the toner. When image output is complete, the sheet S on which the fixed image has been formed is discharged via a pair of discharge rollers 10 to a discharge tray 30 protruding outward from the apparatus main body 1A. When an image is to be formed on the back side of the sheet S in double-sided printing, the sheet S that has passed through the fixing unit 29 has its front and back sides swapped by a reversing unit 39 and is conveyed to a pair of registration rollers 36 by a double-sided conveying unit 40. Then, the sheet S on which the image has been formed again by the image forming unit 33 is discharged to the discharge tray 30.

[0020] [Image reader] The image reading device 5, located above the device body 1A of the image forming apparatus 1, includes a scanner unit 100 and an ADF 200 (Auto Document Feeder), and optically scans a document to read image information. The image information converted into an electrical signal by the image reading device 5 is transferred to a control unit 32 provided in the device body 1A via a controller 500 (see FIG. 3). As a result, the image forming apparatus 1 forms an image on a recording medium based on the image information read by the image reading device 5.

[0021] 2 is a cross-sectional view showing an example of an image reading device 5 of this embodiment. The scanner unit 100 has a front surface reading unit 101, a white reference member 108, a platen glass 109, a reading movement guide 110, a timing belt 151, a platen motor 169, etc. The scanner unit 100 reads an image by driving the platen motor 169 and reading the front surface reading unit 101 line by line of the front surface of a document placed on the platen glass 109 while moving the front surface reading unit 101 along the reading movement guide 110 via the timing belt 151.

[0022] The front surface reading unit 101 is an example of an image reading unit, and reads an image formed on a sheet transported by the feeding unit 7. For example, a contact image sensor (hereinafter referred to as CIS) is used as the front surface reading unit 101. The front surface scanning glass 106 reads an image of a document transported onto the front surface scanning glass 106 by the ADF 200.

[0023] The ADF 200 has a feeding unit 7 which is an example of a sheet conveying device, a pair of registration rollers 215, a back-side reading section 230, an output tray 225, etc. The feeding unit 7 has a document tray 201 which is an example of a loading section for loading a document stack consisting of one or more documents, a guide width regulating plate 202, a width detection sensor 205, a conveying section 240, a sensor section 241, etc. The conveying section 240 has a separation roller 211 and a pickup roller 210, and separates the sheets S loaded on the document tray 201 one by one and conveys them in the conveying direction.

[0024] A guide width regulating plate 202 is installed on the document tray 201 and swings in a width direction (main scanning direction) perpendicular to the document transport direction to regulate the movement of the document in the main scanning direction. A width detection sensor 205 acquires width information in response to the swing of the guide width regulating plate 202. A separation roller 211 and a pickup roller 210 are a separation mechanism that separates documents one by one, and regulates the document stack from protruding beyond the document tray 201 and advancing downstream before the document transport begins. The pickup roller 210 is dropped onto the top of the document stack loaded on the document tray 201 and rotated, thereby transporting the topmost document of the document stack. Of the documents transported by the pickup roller 210, the separation roller 211 separates and transports the topmost sheet. This separation is achieved using a known separation technique.

[0025] When the document separated by separation roller 211 turns on separation sensor 212, a timer count is started. This count is used as a value for calculating the detection start timing of multi-feed detection sensor 213 and for calculating the document length. When the document subsequently reaches the vicinity of multi-feed detection sensor 213, multi-feed detection begins. The document then passes through registration sensor 214 and is transported to registration roller pair 215, where it abuts against the nip position of registration roller pair 215. The leading edge of the abutted document forms a loop, thereby eliminating skew during document transport.

[0026] 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 disposed downstream of the separation sensor 212 in the conveying direction. The first sheet detection sensor 228a detects the sheet conveyed by the conveying unit 240 at a first detection position. The second sheet detection sensor 228b detects the sheet conveyed by the conveying unit 240 at a second detection position, which is a position different from the first detection position in the width direction perpendicular to the conveying direction. The first sheet detection sensor 228a and the second sheet detection sensor 228b detect the skew angle of the leading edge of the document relative to the topmost document in the document stack separated and fed from the document tray 201 by the conveying unit 240. In this embodiment, the separation sensor 212 is an example of a third sensor, and detects the sheet conveyed by the conveying unit 240 at a third detection position, which is a position different from the first and second detection positions in the conveying direction. In this embodiment, the first sheet detection sensor 228a, the second sheet detection sensor 228b, and the separation sensor 212 constitute a sensor unit 241.

[0027] A transport path is arranged downstream of the pair of registration rollers 215 to transport the document that has passed through the pair of registration rollers 215 toward the front side flow reading glass 106. When the document sent to the transport path turns on the lead sensor 216, this triggers timer 171 (see FIG. 3, which will be described later) to count down until 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 up to count down until the leading edge of the document reaches the back side document reading position 220. The document is then transported to the front side document reading position 107 by the pair of lead rollers 217.

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

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

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

[0031] [Control system] 3 is a block diagram showing a control system of the image reading device 5 of this embodiment. The image reading device 5 includes a CPU 164, which is a central processing unit, a ROM 165, which is a read-only memory, and a RAM 166, which is a 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 of the LEDs 102 and 231. The scanning control unit 168 controls the driving of a platen motor 169. The platen motor 169 is connected to the front surface reading unit 101 by a timing belt 151 or the like, and when the platen motor 169 is driven, the front 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 driving of a document transport motor 170 built into the ADF 200. The document transport motor 170 is connected to a separation roller 211, a pair of registration rollers 215, a pair of read rollers 217, a pair of read rollers 219, a pair of read rollers 221, a pair of discharge rollers 223, etc. When the document transport motor 170 is driven, these rollers rotate, and the document is transported to a transport path within the ADF 200.

[0033] The front surface line sensor 103 is built into the front surface reading unit 101 and receives light that is irradiated by the front surface LED 102 and reflected from the original. This light is input to the A / D conversion unit 161, where the analog data is converted into digital data. The image processing unit 162 performs image processing to generate image data. Similarly, the back surface line sensor 232 is built into the back surface reading unit 230 and receives light that is irradiated by the back surface LED 231 and reflected from the original. The subsequent processing is the same as for the front surface side, so a description thereof will be omitted. The original size acquisition unit 163 acquires original size information to be read input by an operation unit 506 of the controller 500, which will be described later, and acquires original size information from a combination of the states of the width detection sensor 205 and the length detection sensor 206.

[0034] The shading RAM 254 is composed of an arithmetic memory 255 and a coefficient memory 256, and is accessible for reading and writing from the CPU 164. The nonvolatile 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 retain shading target values ​​when shading correction is performed by the shading correction circuit 253, or alarm and error information that occurs during a job.

[0035] The timer 171 receives and counts pulse signals transmitted at predetermined distances as the document transport motor 170 is driven, and transmits a timer expiration signal to the CPU 164 when a preset count value is reached. This makes it possible to measure the distance the document has traveled. The front image reading control unit 172 performs image reading processing. When the timer value set in the timer 171 expires and the CPU 164 receives the signal, the signal is transmitted as a trigger signal to the front image reading control unit 172 and the back image reading control unit 173. Based on this trigger, the front 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, and when the leading edge of the document reaches each sensor or when the trailing edge of the document leaves each sensor, the signal is transmitted to the transport sensor detection unit 174. The CPU 164 receives this signal as an interrupt, making it possible to transmit processing to the timer 171 etc. without delay. The first sheet detection sensor 228a and the second sheet detection sensor 228b detect the skew angle of the leading edge of the document, relative to the topmost document in the document stack separated and fed from the document tray 201.

[0037] The controller 500 converts the document image read by the image reading device 5 into a format that allows the image to be output onto a sheet S set in the image forming apparatus 1. Alternatively, the controller 500 converts the image into a format that allows the image to be output to a PC, and also handles the reception of user operations and the management of the entire apparatus. The image reading device 5 and the controller 500 are connected by a communication line 180, and various data signals between the image reading device 5 and the controller 500 are transmitted and received via the communication line 180. The controller 500 includes a CPU 501 that is a central processing unit, a ROM 502 that is a read-only memory, and a RAM 503 that is a random access memory. The ROM 502 stores control programs for realizing image conversion and overall apparatus management, and the RAM 503 stores input data and working data.

[0038] An image processing unit 504 performs processing to convert the document image read by the image reading device 5 into a format that can be output by the image forming device 1. The image data is temporarily stored in an image memory 505. An operation unit 506 is composed of a touch panel on which a screen and operation buttons are installed, and in addition to accepting button operations from the user, outputs various information to the user on the screen.

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

[0040] [Skew detection] Generally, the ADF 200 cannot separate and feed so-called "bound sheets," such as stapled or glued sheets. Such sheets may be damaged by the separation operation by the separation roller 211 and separation pad 226. In the case of sheets that are bound at one end in the sheet width direction, the separation operation causes the leading edge of the first sheet to skew, which then causes the sheet to be damaged. Therefore, in this embodiment, the first sheet detection sensor 228a and the second sheet detection sensor 228b provided in the feeding and conveying section of the ADF 200 detect skew in the sheet and stop the feeding and conveying process at that point, thereby preventing damage to the sheet.

[0041] FIGS. 4(a) to 4(d) are explanatory diagrams showing a portion of the ADF 200 when attempting to feed and convey a sheet bound at one end in the sheet width direction. FIGS. 4(a) and 4(c) are cross-sectional views of the ADF 200, and FIGS. 4(b) and 4(d) are plan views of the conveyance path of the ADF 200. The dashed lines between FIGS. 4(a) and 4(b) and between FIGS. 4(c) and 4(d) indicate the positions of sensors, rollers, and the like in the two figures. Similarly, FIGS. 5(a) to 5(f) are explanatory diagrams showing a portion of the ADF 200 when attempting to feed and convey a normal sheet in a tilted state. FIGS. 5(a), 5(c), and 5(e) are cross-sectional views of the ADF 200, and FIGS. 5(b), 5(d), and 5(f) are plan views of the conveyance path of the ADF 200. The dashed lines between Figures 5(a) and 5(b), between Figures 5(c) and 5(d), and between Figures 5(e) and 5(f) indicate the corresponding positions of each sensor, roller, etc. in the two figures.

[0042] A first sheet detection sensor 228a and a second sheet detection sensor 228b are connected to the sheet detection sensor acquisition unit 228 (see FIG. 3). The first sheet detection sensor 228a and the second sheet detection sensor 228b are sensors for detecting the leading edge of a sheet, and are configured, for example, by photosensors. As shown in FIG. 4(b), the first sheet detection sensor 228a and the second sheet detection sensor 228b are arranged side by side at an interval in the sheet width direction, sandwiching the separation roller 211 therebetween. Due to this arrangement, when a normal sheet (a sheet that is not bound) is not skewed, the first sheet detection sensor 228a and the second sheet detection sensor 228b detect the leading edge of the sheet almost simultaneously.

[0043] In the case of stapled sheets, if the leading edge of the first sheet is skewed due to the separation operation, one sensor detects the leading edge of the sheet first, and then the stapled sheet stack cannot be transported downstream of the separation roller 211, and the other sensor does not detect the leading edge of the sheet. In the example of FIG. 4, the second sheet detection sensor 228b detects the leading edge of the sheet as shown in FIG. 4(b). As the sheet feeding and conveyance progresses, the first sheet becomes more skewed due to the separation operation as shown in FIG. 4(d), but the first sheet detection sensor 228a still does not detect the leading edge of the sheet. If the sheet feeding and conveyance continues in this state, the sheet will be damaged.

[0044] On the other hand, in the case of a normal sheet that is skewed, there is a time lag between when one sensor detects the leading edge of the sheet and when the other sensor detects the leading edge of the sheet. In the example of Fig. 5, the second sheet detection sensor 228b detects the leading edge of the sheet as shown in Fig. 5(b). As the sheet continues to be fed, the first sheet detection sensor 228a detects the leading edge of the sheet as shown in Fig. 5(d).

[0045] 4 and 5, the approximate amount of skew occurring in the sheet can be calculated from the time elapsed since one sensor detected the leading edge of the sheet. The sheet conveying speed is V [mm / s], and the widthwise distance between the first sheet detection sensor 228a and the second sheet detection sensor 228b is W [mm]. Furthermore, the time elapsed from when one sensor detects the leading edge of the sheet until the other sensor detects the leading edge of the sheet is t [s], and the amount of skew occurring in the sheet is θ0. In this case, the following formula 1 holds: t = W × tanθ0 ÷ V (Equation 1)

[0046] In this embodiment, if the sheet S is skewed by 3° or more, it is determined that there is a risk of the sheet being damaged by the separation operation of the bound sheets, and the sheet conveyance process is stopped and the document conveyance motor 170 is stopped. That is, in this case, Equation 2 is derived as the relational expression. tθ = W × tanθ ÷ V (Equation 2)

[0047] In formula 2, if one sheet detection sensor does not detect the leading edge of the sheet until time t3° has elapsed since the other sheet detection sensor detected the leading edge of the sheet, it is determined that a skew of 3° or more has occurred, and the conveying process is stopped. In other words, a determination is made even if the sheet is detected by only one of the first sheet detection sensor 228a and the second sheet detection sensor 228b.

[0048] As shown in Figure 4(d), when bound sheets are fed and conveyed, skew that occurs at the leading edge of the sheet is characterized by the fact that the amount of skew is small near the edge on the side where the bound portion is located and large near the other edge. Therefore, when detecting bound sheets by skew detection, it is desirable to position the sensor used for skew detection close to the edge in the width direction of the sheet. By positioning the sensor used for skew detection close to the edge in the width direction of the sheet, skew that occurs at the leading edge of the bound sheet on the side other than the bound portion can be detected regardless of whether the bound portion is located at the rear or front side in the width direction.

[0049] 5(e) and 5(f), in this embodiment, the first sheet detection sensor 228a and the second sheet detection sensor 228b are disposed in positions close to the widthwise ends of the sheet when the minimum size sheet is fed and conveyed. This makes it possible to detect skew even when a skew of 3° occurs in a sheet of the minimum size that can be conveyed by the ADF 200.

[0050] Here, as mentioned above, while skew detection is useful for preventing damage to bound sheets, since it determines whether a sheet is bound or not based on the detection time difference between the sheet detection sensors on both ends, the sheet feeding and conveying process may be stopped for documents other than bound sheets. For example, when placing a stack of documents on document tray 201, if the documents are placed roughly set without aligning one edge, the state shown in Figures 5(a) and (b) will occur, and the document cannot be distinguished from a bound sheet, so the sheet feeding and conveying process will be stopped.

[0051] [Operation panel display when skew is detected] 6 shows an example of the display content displayed on the operation unit 506 when the sheet detection sensor acquisition unit 228 determines that the conveyed document is skewed. This screen is displayed on the operation unit 506 at the same time that the sheet feeding and conveying process is stopped. When it is determined that the document is skewed, a message is displayed that lists possible causes of the stop, as described above, and guides the user to the next measure to be taken. If the conveyed 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 conveyance path in the ADF 200, including the bound sheet. The user then removes the bound sheet or removes the binding medium, such as staples, and places the document stack on the document tray 201 again, and starts the job again.

[0052] If the originals actually transported are not bound sheets and are of the same width, it is possible that the originals were placed at an angle when placed on the original tray 201, or that the originals are prone to skew due to wrinkles or creases. If the originals are placed in a rough set state, where one edge of the originals is not aligned, it is sufficient to realign at least one edge of the original stack and then place them on the original tray 201 again. However, if the originals are prone to skew, the sheet detection sensor acquisition unit 228 may again determine that the originals are skewed if the originals are transported again, and transport may be interrupted. Since the originals cannot be read in this state, to enable this, the user presses button 506a, which temporarily turns off skew detection. Pressing this button stores information to RAM 503. When the originals are transported in this state, the information in RAM 503 is transmitted to CPU 164 via communication line 180, and the sheet detection sensor acquisition unit 228 does not detect the originals during transport, or, even if it does detect them, does not calculate or determine the amount of skew. Therefore, the job is not interrupted and the document stack can be read.

[0053] Here, the document transport speed may be slower than expected due to wear of the transport unit 240, such as the pickup roller 210, or the adhesion 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, resulting in an overcalculated amount of skew of the sheet. In this case, even if the amount of skew is actually below the threshold for stopping transport, it may be erroneously determined to be above the threshold. 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.

[0054] [Control Flow] Next, the control flow of the image reading device 5 in a flow reading job will be described with reference to Figures 7, 8, and 9. Figure 7 is a flowchart of control in this embodiment, from receiving a flow reading start request, to calculating the transport efficiency, detecting skew based on the calculated efficiency, reading the document image, and transmitting the image to the controller 300. The processing shown in Figure 7 is performed by the CPU 164 of the control unit 160 executing a program stored in the ROM 165.

[0055] When the control unit 160 starts the flow reading job processing, it starts conveying the sheet (S101). The control unit 160 determines whether or not 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 or not 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).

[0056] When 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 calculates the conveying efficiency (S104). The conveying efficiency calculation process will be described later with reference to FIG. 8. The control unit 160 determines whether or not to perform skew detection based on the calculation result of the conveying efficiency (S105). When the control unit 160 determines to perform skew detection (S105; YES), it performs skew detection and calculates the amount of skew θ of the sheet (S106).

[0057] The control unit 160 determines whether the skew amount θ exceeds the product of the threshold value T and the correction value A (S107). The threshold value T here is set in advance to a skew amount at which it is considered difficult to read the sheet correctly, and in this embodiment, T=3°. The correction value A will be described later with reference to FIG. 8. If the control unit 160 determines that the skew amount θ exceeds the product of the threshold value T and the correction value A (S107; YES), the control unit 160 stops conveying the sheet by the conveying unit 240 (S130) because there is a risk of sheet damage.

[0058] If the control unit 160 determines that the skew amount θ does not exceed the product of the threshold value T and the correction value A (S107; NO), it considers that the document is being fed normally. If the control unit 160 determines that the skew amount θ does not exceed the product of the threshold value T and the correction value A (S107; NO), or if it determines in S105 that skew detection will not be performed, 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 sheet has reached the reading position (S108; YES), it performs image reading processing (S109). After reading the image, the control unit 160 performs correction by image processing as necessary as described above, and then transmits the image to the controller 300 (S110). When the transfer of one image for one sheet is completed, the reading processing for one sheet is completed.

[0059] 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 transmits the images to the controller 300 again (S110). If the control unit 160 determines that the transfer of all images has been completed (S111; YES), it determines whether the next sheet is on the document tray 201 (S112). If the control unit 160 determines that the next sheet is 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), since the reading process of all sheets has been completed, it stops conveyance after conveying the final sheet (S113) and ends the job.

[0060] In this embodiment, the control unit 160 calculates the conveying efficiency E (S201, described later) and calculates a correction value A for the skew detection threshold from the calculated conveying efficiency E (S202, described later). As described later, the conveying efficiency E indicates the ratio of a reference conveying time to the time difference between the detection times of the first sheet detection sensor 228a and the second sheet detection sensor 228b, and is synonymous with the actual conveying speed relative to the reference conveying speed. In other words, the threshold T can be said to change depending on the actual conveying speed. Furthermore, the threshold T is corrected by multiplying the threshold T by the correction value A, and the corrected threshold T is compared with the skew amount θ. Here, the comparison target with the threshold T is shown as the skew angle θ, but the control unit 160 calculates the skew angle θ based on the elapsed time since detection by one of the two sheet detection sensors, the first sheet detection sensor 228a and the second sheet detection sensor 228b. In other words, the comparison target with the threshold T can also be the elapsed time, and the threshold can be a threshold for elapsed time rather than an angle.

[0061] In this embodiment, the control unit 160 determines whether the skew amount θ exceeds the product of the threshold value T and the correction value A (S107). In contrast, the skew amount θ essentially correlates with the elapsed time since detection by one of the two sheet detection sensors, the first sheet detection sensor 228a and the second sheet detection sensor 228b, the threshold value T correlates with the threshold time T0, and the correction value A correlates with the sheet speed. Therefore, the control unit 160 determines whether the elapsed time since detection by one of the two sheet detection sensors, the first sheet detection sensor 228a and the second sheet detection sensor 228b, exceeds the threshold time T0, which is changed based on the sheet speed. In this case, the control unit 160 lengthens the threshold time T0 if the sheet speed slows. That is, when the sheet speed is a first speed V1, the control unit 160 sets the threshold time T0 to a first time T1. When the sheet speed is a second speed V2, which is slower than the first speed V1, the control unit 160 sets the threshold time T0 to a second time T2, which is longer than the first time T1.

[0062] Furthermore, the control unit 160 measures the time since one of the first sheet detection sensor 228a and the second sheet detection sensor 228b detected the sheet. Then, if the other of the first sheet detection sensor 228a and the second sheet detection sensor 228b does not detect the sheet before the threshold time T0 has elapsed (corresponding to S107; YES), the control unit 160 stops the conveyance of the sheet by the conveyance unit 240 (S130). This is the first stop process.

[0063] [Calculation of transport efficiency] FIG. 8 is a control flowchart for calculating the conveyance efficiency and determining whether to perform skew detection processing based on the calculated conveyance efficiency. The processing shown in FIG. 8 is performed by the CPU 164 of the control unit 160 executing a program stored in the ROM 165. The control unit 160 calculates the conveyance efficiency E based on the time difference between when the separation sensor 212 and one of the first sheet detection sensor 228a and the second sheet detection sensor 228b turn on (S201). The conveyance efficiency E is calculated as E = (reference conveyance time) / (time difference) × 100. The reference conveyance time is the value obtained by dividing the distance between the sensors by the reference conveyance speed of the sheet in that section. In this embodiment, for example, it is calculated as 10 mm / 350 mm / s × 100 = 28.6 ms. In addition, in this embodiment, the control unit 160 calculates the conveyance efficiency E based on the measured value of the sheet speed obtained by one speed detection processing. This allows for rapid skew detection according to the current reading situation.

[0064] Here, the conveying efficiency E indicates the ratio of the reference conveying time to the time difference between the detection times of the first sheet detection sensor 228a and the second sheet detection sensor 228b, and is synonymous with the ratio of the actual conveying speed to the reference conveying speed. Therefore, in S201, the control unit 160 can be said to perform a speed detection process that measures the speed of the sheet conveyed by the conveying unit 240 based on the detection result of the sensor unit 241. In this embodiment, the control unit 160 performs the speed detection process based on the time difference between the time when one of the first sheet detection sensor 228a and the second sheet detection sensor 228b detects the sheet and the time when the separation sensor 212 detects the sheet S.

[0065] The control unit 160 calculates a correction value A for the skew detection threshold from the calculated conveying efficiency E (S202). The correction value A for skew detection is calculated by A = 100 / E. The control unit 160 determines whether the conveying efficiency E exceeds the threshold Te for skew detection (S203). The threshold Te for skew detection is a conveying efficiency value at which skew detection can be performed normally, and is set to 50% in this embodiment. In this embodiment, whether the conveying efficiency E exceeds the threshold Te for skew detection is synonymous with whether the actual conveying speed is faster than the threshold speed TV. In other words, if the threshold speed TV is set to 50% of the reference speed, and the actual conveying speed is 50% or less of the reference speed, the control unit 160 determines NO in S203.

[0066] If the control unit 160 determines that the conveying efficiency E exceeds the threshold Te for performing skew detection (S203; YES), it determines that skew detection can be performed normally, sets the job to perform skew detection (S204), and terminates the process of determining whether to perform skew detection.

[0067] If the control unit 160 determines that the conveying efficiency E does not exceed the threshold Te for skew detection (S203; NO), it determines that skew detection cannot be performed normally and stops sheet conveyance (S210). That is, if the measured sheet speed is slower than the threshold speed TV, the control unit 160 executes a second stop process to stop sheet conveyance by the conveyance unit 240 before selecting the first mode or the second mode (S212), which will be described later. This allows conveyance to be stopped immediately if there is a possibility that skew detection cannot be performed normally. The control unit 160 displays a notice (see FIG. 9) on the operation unit 506 to warn that skew detection cannot be performed normally (S211). FIG. 9 shows an example of the display content displayed on the operation unit 506 when it is determined that the conveyance efficiency of the feeding unit has decreased. When the control unit 160 stops the sheet feeding and conveyance process, it promptly displays this screen on the operation unit 506.

[0068] The control unit 160 waits for the user's input as to whether or not to perform skew detection (S212). That is, when the measured sheet speed is slower than the threshold speed TV, the control unit 160 can selectively execute a first mode in which the first stop process (skew detection) is executed, or a second mode in which the first stop process (skew detection) is not executed. If the user determines that skew detection is executed and presses the resume button 506d (S212; YES), the first mode is selected, and skew detection is set to be executed for this job (S213). On the other hand, if the user determines that skew detection is not executed and presses the button 506c to temporarily turn off skew detection (S212; NO), the second mode is selected, and skew detection is set not to be executed for this job (S220). In this way, after the second stop process (S210) is executed, the control unit 160 executes the selected mode after the first mode or the second mode is selected. In order to resume reading, the control unit 160 displays an instruction to place sheets that are being conveyed or have already been ejected back onto the document tray 201 (S214), resumes sheet conveyance (S215), and ends the skew detection execution determination process. Note that in this embodiment, when the second mode is selected, skew detection is not performed only during the job. Therefore, when the job ends and another job is executed, the selection of the first mode and the second mode is reset.

[0069] As described above, according to the image forming apparatus 1 of this embodiment, the control unit 160 stops conveying the sheet when the skew amount θ is greater than the threshold value T corrected by the correction value A (S130). As a result, even if the document conveying speed becomes slower than expected due to wear of the conveying unit 240 or adhesion of paper dust, by using the correction value A that reflects the actual conveying speed, it is possible to suppress erroneous detection of the skew amount θ and make a highly accurate decision to stop the sheet.

[0070] In this embodiment, when the control unit 160 determines that the conveying efficiency E does not exceed the threshold Te for skew detection (S203; NO), it determines that skew detection cannot be performed normally and stops the sheet conveyance (S210). This allows the conveyance to be stopped immediately when there is a possibility that skew detection cannot be performed normally.

[0071] In this embodiment, when the measured sheet speed is slower than the threshold speed TV, the control unit 160 can selectively execute a first mode in which the first stop process (skew detection) is executed, or a second mode in which the first stop process (skew detection) is not executed. Therefore, the user can select an appropriate process depending on whether to prioritize sheet skew detection or to prioritize reading speed without skew detection.

[0072] [Other embodiments] In the above-described embodiment, both the correction of the skew detection threshold based on the conveyance efficiency (S107) and the determination of whether to perform skew detection (S212) are applied. However, this is not limited thereto, and only one of these controls may be applied. For example, if the correction of the skew detection threshold is not executed (S107), the control unit 160 calculates the conveyance efficiency (S104) and then waits for the sheet to reach the reading start position (S108). In this case, the flow shown in FIG. 8 is executed in S104. Therefore, if the measured sheet speed is slower than the threshold speed TV, the control unit 160 executes a second stop process to stop the sheet conveyance by the conveyance unit 240. After executing the second stop process, the control unit 160 selectively executes a first mode in which the first stop process is executed and a second mode in which the first stop process is not executed. After the first mode or the second mode is selected, the control unit 160 executes the selected mode. On the other hand, if the determination of whether to perform skew detection (S212) is not performed, the determination of whether the conveying efficiency E exceeds the threshold Te for performing skew detection (S203) is not performed, or a warning is displayed (S211), and the first mode and the second mode are not selected.

[0073] [Flow using average values] In the above embodiment, the control unit 160 calculates the conveying efficiency E based on the measured value of the sheet speed obtained by one speed detection process (S201), but this is not limiting. For example, the control unit 160 may execute the speed detection process multiple times and calculate the average conveying efficiency Ea based on the average value calculated from the measured value of the sheet speed obtained by each speed detection process.

[0074] The processing procedure in this case will be described with reference to Fig. 10. Fig. 10 is a flowchart of a process for calculating the average conveying efficiency Ea and determining whether or not to perform the skew detection process based on the calculated efficiency. The process shown in Fig. 10 is performed by the CPU 164 of the control unit 160 executing a program stored in the ROM 165.

[0075] The control unit 160 calculates the conveying efficiency E based on the time difference between when the separation sensor 212 and one of the first sheet detection sensor 228a and the second sheet detection sensor 228b turn on (S301). The control unit 160 calculates the average conveying efficiency Ea from the calculated conveying efficiency E (S302). The average conveying efficiency Ea is the average of the conveying efficiencies calculated the past N times, where N=10 in this embodiment. The average conveying efficiency may be calculated separately depending on the type or basis weight of the conveyed sheet. The control unit 160 calculates a correction value A for the skew detection threshold from the calculated average conveying efficiency Ea (S303). The correction value A for skew detection is calculated by A=100 / Ea.

[0076] The control unit 160 determines whether the average conveying efficiency Ea exceeds the threshold Te for performing skew detection (S304). If the control unit 160 determines that the average conveying efficiency Ea exceeds the threshold Te for performing skew detection (S304; YES), it determines that skew detection can be performed normally, sets the job to perform skew detection (S305), and ends the skew detection performance determination process. If the control unit 160 determines that the average conveying efficiency Ea does not exceed the threshold Te for performing skew detection (S304; NO), it determines that skew detection cannot be performed normally, and stops sheet conveyance (S310). The processes from S310 to S320 are the same as S210 to S220 in FIG. 8, and therefore description thereof will be omitted.

[0077] In the embodiment shown in Fig. 10 described above, the skew detection threshold value can be corrected and a determination as to whether skew detection should be performed can be made based on the calculated average value of the conveying efficiency. This makes it possible to realize a highly accurate determination with less influence of disturbances than when a determination is made based on only one measurement value. Note that, in this embodiment, a case has been described in which both the correction of the skew detection threshold value based on the average conveying efficiency and the determination as to whether skew detection should be performed are performed, but this is not limiting, and it is also possible to apply control of only one of them.

[0078] [Flow for automatically switching from 2nd mode to 1st mode] In the above-described embodiment, when the user selects the second mode, which does not perform skew detection (S212; NO), the second mode continues to perform skew detection only for this job. However, this is not limited to this. For example, the second mode may continue to not perform skew detection even if the job changes until the user switches to the first mode. In this case, when a predetermined condition is met, such as the sheet speed recovering, the mode may automatically switch to the first mode and resume skew detection. The processing procedure for this case will be described with reference to FIG. 11.

[0079] 11 shows an embodiment in which, when the second mode in which skew detection is not performed using the average conveying efficiency Ea is selected in S320 of FIG. 10, the second mode is continued and skew detection is stopped until the restart condition is met. In this embodiment, a process for automatically switching from the second mode to the first mode when the restart condition is met will be described. FIG. 11 is a flowchart of a process for determining whether to restart the skew detection process. The process shown in FIG. 11 is performed by the CPU 164 of the control unit 160 executing a program stored in the ROM 165. In this embodiment, the skew detection restart determination for switching from the second mode to the first mode is performed when the image reading device 5 is started up.

[0080] In the process of determining whether to resume skew detection, the control unit 160 determines whether a feeding component has been replaced (S401). In this embodiment, after replacing a feeding component, the user performs an operation on the operation unit 506 to clear the consumption information of the feeding component stored in the RAM 503. This operation causes information that the feeding component has been replaced to be stored in the RAM 503. When the control unit 160 determines by referring to the information in the RAM 503 that the feeding component has been replaced (S401; YES), it determines that the decrease in conveying efficiency has been resolved and resumes skew detection (S402).

[0081] The control unit 160 refers to the information in the RAM 503 and, if it determines that the feeding components have not been replaced (S401; NO), determines whether the average conveying efficiency Ea exceeds the threshold value Tb. The threshold value Tb here is the conveying efficiency at which it is determined that the conveying efficiency has improved due to some factor and that it is okay to resume skew detection, and is set to 90% in this embodiment. If the control unit 160 determines that the average conveying efficiency Ea exceeds the threshold value Tb (S410; YES), it resumes skew detection (S402). If the control unit 160 determines that the average conveying efficiency Ea does not exceed the threshold value Tb (S410; NO), it does not resume skew detection and ends the skew detection resumption determination process. In this way, after the second mode is selected, if the speed of the sheet S conveyed by the conveying unit 240 becomes equal to or greater than the threshold speed, the control unit 160 automatically switches from the second mode to the first mode and executes the second mode.

[0082] 11, when the second mode in which skew detection is not performed is selected, skew detection is stopped continuously until the restart condition is met, but the mode can be automatically switched to the first mode to restart skew detection. As a result, even if the user forgets to switch the setting to the first mode in a situation where skew detection is normally possible, the mode is automatically switched to the first mode, so skew detection can be performed.

[0083] In this embodiment, control is performed based on the average conveying efficiency Ea, but control may also be performed based on a single conveying efficiency E, which is not an average. In this embodiment, the determination of whether to resume skew detection is performed when the image reading device 5 is started, but this is not limited to this and can be set appropriately, for example, when starting a new job. In this embodiment, after replacing a feeding part, the user performs an operation to clear the wear information of the feeding part stored in RAM 503 from the operation unit 506, but this is not limited to this. For example, the control unit 160 may automatically acquire the part replacement history and automatically record it in RAM 503.

[0084] [Speed ​​detection process without using a sheet detection sensor] In the above-described embodiment, of the two sensors for detecting the sheet speed used to calculate the conveying efficiency E, the first sheet detection sensor 228a or the second sheet detection sensor 228b is used to detect skew, but this is not limiting. For example, a speed detection sensor may be provided at the same position in the conveying direction as the first sheet detection sensor 228a and the second sheet detection sensor 228b, and the speed may be detected by this sensor and the separation sensor 212.

[0085] Alternatively, the speed may be detected using the separation sensor 212 and the pull-out sensor 227. The pull-out sensor 227 is an example of a fourth sensor, and detects the sheet conveyed by the conveying unit 240 at a fourth detection position that is different from the third detection position in the conveying direction. The sensor unit 241 also has a first sheet detection sensor 228a, a second sheet detection sensor 228b, the separation sensor 212, and the pull-out sensor 227. In this case, since the pull-out sensor 227 is disposed downstream of the first sheet detection sensor 228a and the second sheet detection sensor 228b in the conveying direction, the determination using the detection result of the skew detection is delayed until the conveying speed (conveying efficiency E) is calculated. The processing procedure in this case will be described below.

[0086] [Flow to delay skew detection until transport efficiency calculation] 12 is a flowchart showing how the conveyance efficiency is calculated using the separation sensor 212 located upstream of the first sheet detection sensor 228a and the second sheet detection sensor 228b used for skew detection, and the pull-out sensor 227 located downstream of the first sheet detection sensor 228a and the second sheet detection sensor 228b used for skew detection, and how skew detection is controlled based on the calculated conveyance efficiency. The processing shown in FIG. 12 is performed by the CPU 164 of the control unit 160 executing a program stored in the ROM 165.

[0087] Next, an embodiment in which a determination using the detection result of skew detection is delayed until the conveyance efficiency is calculated will be described with reference to FIG. 12. When the control unit 160 starts the flow reading job process, it starts conveying the sheet (S501). The control unit 160 determines whether the sheet has reached the separation sensor 212 (S502). If the control unit 160 determines that the sheet has not reached the separation sensor 212 (S502; NO), it makes a determination again (S502). If the control unit 160 determines that the sheet has reached the separation sensor 212 (S502; YES), it performs skew detection and calculates the skew amount θ of the sheet (S503). At this point, the skew amount θ of the sheet is calculated, but the control unit 160 does not determine whether to stop conveying the sheet using the skew amount until the calculation of the conveyance efficiency is completed.

[0088] The control unit 160 determines whether the sheet has reached the pull-out sensor 227 (S504). If the control unit 160 determines that the sheet has not reached the pull-out sensor 227 (S504; NO), it makes the determination again (S504). If the control unit 160 determines that the sheet has reached the pull-out sensor 227 (S504; YES), it calculates the conveying efficiency (S505).

[0089] The control unit 160 determines whether or not to perform skew detection based on the calculation result of the conveyance efficiency (S506). If the control unit 160 determines to perform skew detection (S506; YES), it determines whether or not to stop conveying the sheet based on the skew detection result (S507). If the control unit 160 determines not to perform skew detection (S506; NO), it waits for the sheet to reach the reading start position (S508). Note that the processes from S507 to S531 are the same as S107 to S131 in FIG. 7, and therefore description thereof will be omitted.

[0090] That is, in this flow, the control unit 160 first acquires a second time difference between the time when the first sheet detection sensor 228a detects the sheet S and the time when the second sheet detection sensor 228b detects the sheet (S503). Then, the control unit 160 executes a speed detection process based on the first time difference between the time when the separation sensor 212 detects the sheet and the time when the pull-out sensor 227 detects the sheet (S505). The control unit 160 changes the threshold time based on the sheet speed obtained by the speed detection process (S507). If the second time difference exceeds the changed threshold time (S507; YES), the control unit 160 executes a first stop process to stop sheet conveyance (S530).

[0091] 12, even in a sensor configuration in which calculation of conveyance efficiency is slower than skew detection processing, by waiting for a judgment using the skew detection result, it is possible to correct the skew detection threshold based on conveyance efficiency and to execute a judgment using the skew detection result, thereby increasing the degree of freedom in the sensors that can be used.

[0092] In this embodiment, the case where both the correction of the skew detection threshold value based on the conveying efficiency and the determination of whether to perform skew detection are described, but this is not limited to this, and control of only one of them may be applied. Also, when the user determines not to perform skew detection, skew detection may be continuously prevented from being performed until the user sets a restart, not limited to this job.

[0093] In each of the above-described embodiments, the sheet conveying device is applied to the feeding unit 7 of the image reading device 5, but the present invention is not limited to this. The sheet conveying device of the present invention can be applied to all sheet conveying devices that convey sheets in the image reading device 5 and the image forming device 1. [Explanation of symbols]

[0094] 1...image forming apparatus, 5...image reading device, 7...feeding unit (sheet conveying device), 33...image forming section, 101...surface reading section (image reading section), 160...control section, 201...document tray (loading section), 212...separation sensor (third sensor), 227...pulling sensor (fourth sensor), 228a...first sheet detection sensor (first sensor), 229b...second sheet detection sensor (second sensor), 240...conveying section, 241...sensor section, S...sheet

Claims

1. a loading section on which sheets are loaded; a conveying section that separates the sheets stacked on the stacking section one by one and conveys them in a conveying direction; a sensor unit including a first sensor that detects the sheet conveyed by the conveying unit at a first detection position and a second sensor that detects the sheet at a second detection position that is different from the first detection position in a width direction perpendicular to the conveying direction; a control unit capable of executing a first stop process of stopping conveyance of the sheet by the conveying unit when one of the first sensor and the second sensor does not detect the sheet until a threshold time has elapsed since the other of the first sensor and the second sensor detected the sheet; and a speed detection process of measuring a speed of the sheet conveyed by the conveying unit based on a detection result of the sensor unit, the control unit sets the threshold time to a first time when the sheet speed measured in the speed detection process is a first speed, and sets the threshold time to a second time longer than the first time when the sheet speed measured in the speed detection process is a second speed slower than the first speed. A sheet conveying device characterized by:

2. the sensor unit includes a third sensor that detects the sheet conveyed by the conveying unit at a third detection position that is a position different from the first detection position and the second detection position in the conveying direction, the control unit executes the speed detection process based on a time difference between a time when one of the first sensor and the second sensor detects the sheet and a time when the third sensor detects the sheet.

2. The sheet transport device according to claim 1.

3. the sensor unit includes a third sensor that detects the sheet conveyed by the conveying unit at a third detection position, and a fourth sensor that detects the sheet at a fourth detection position that is a position different from the third detection position in the conveying direction, the control unit executes the speed detection process based on a first time difference between a time when the third sensor detects the sheet and a time when the fourth sensor detects the sheet.

2. The sheet transport device according to claim 1.

4. the fourth detection position is disposed downstream of the first detection position and the second detection position in the conveying direction, The control unit acquiring a second time difference between the time when the first sensor detects the sheet and the time when the second sensor detects the sheet; performing the speed detection process based on the first time difference; changing the threshold time based on the sheet speed obtained by the speed detection process; When the second time difference exceeds the changed threshold time, the first stop process is executed.

4. The sheet transport device according to claim 3.

5. the control unit selectively executes a first mode in which the first stop process is executed and a second mode in which the first stop process is not executed when the measured sheet speed is slower than a threshold speed.

2. The sheet transport device according to claim 1.

6. The control unit If the measured sheet speed is slower than the threshold speed, a second stop process is executed to stop the sheet conveyance by the conveyance unit before selecting the first mode and the second mode. After the second stop process is executed, the first mode or the second mode is selected, and then the selected mode is executed.

6. The sheet transport device according to claim 5.

7. the control unit automatically switches the second mode to the first mode when the speed of the sheet conveyed by the conveying unit becomes equal to or higher than the threshold speed after the second mode is selected.

6. The sheet transport device according to claim 5.

8. the control unit changes the threshold time based on a measurement value of the sheet speed obtained by one of the speed detection processes.

2. The sheet transport device according to claim 1.

9. the control unit executes the speed detection process a plurality of times, and changes the threshold time based on an average value calculated from the measured values ​​of the sheet speeds obtained in the respective speed detection processes.

2. The sheet transport device according to claim 1.

10. a loading section on which sheets are loaded; a conveying section that separates the sheets stacked on the stacking section one by one and conveys them in a conveying direction; a sensor unit including a first sensor that detects the sheet conveyed by the conveying unit at a first detection position and a second sensor that detects the sheet at a second detection position that is different from the first detection position in a width direction perpendicular to the conveying direction; a control unit that is capable of executing a first stop process of stopping conveyance of the sheet by the conveyance unit in response to a detection result of detecting skew of the sheet based on a detection result of the sensor unit, and a speed detection process of measuring a speed of the sheet conveyed by the conveyance unit based on the detection result of the sensor unit, the control unit selectively executes a first mode in which the first stop process is executed and a second mode in which the first stop process is not executed when the measured sheet speed is slower than a threshold speed. A sheet conveying device characterized by:

11. The control unit If the measured sheet speed is slower than the threshold speed, a second stop process is executed to stop the sheet conveyance by the conveyance unit before selecting the first mode and the second mode. After the second stop process is executed, the first mode or the second mode is selected, and then the selected mode is executed.

11. The sheet transport device according to claim 10.

12. The sheet conveying device according to any one of claims 1 to 11, an image reading unit that reads an image formed on the sheet conveyed by the sheet conveying device, An image reading device characterized by:

13. The image reading device according to claim 12; an image forming unit that forms an image on a sheet based on information of the image read by the image reading device, An image forming apparatus characterized by:

Images