Sheet feeding device and image forming device

Abstract

To provide a sheet feeding device capable of recovering delay of a sheet while feeding the following sheet when the following sheet following a preceding sheet delays, and an image forming device provided with the sheet feeding device.SOLUTION: A feeding speed control section 106 times a first elapsed time Ta from a time point T3 when a rear end of a preceding sheet is detected with a sheet detection sensor 51 at a position P1. Then, the feeding speed control section 106 determines whether or not a tip of the following sheet is detected at a time point (reference time) when the first elapsed time Ta reaches a reference time. Further, when the tip of the following sheet is not detected at the reference time, the feeding speed control section 106 changes a feeding speed of the following sheet from an initial speed V1 to a high speed V2 and keeps the feeding speed of the sheet with a downstream side feeding roller 92A at the initial speed V1.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying device capable of conveying a sheet, and an image forming apparatus including the sheet conveying device. [Background technology]

[0002] Image forming devices such as printers, copiers, facsimiles, and multifunction devices equipped with these functions are provided with a registration roller unit having a registration roller pair. The registration roller unit corrects skew of the sheet by waiting with the leading edge of the sheet abutting against the nip portion of the stopped registration roller pair, and then rotates the registration roller pair at a predetermined sending-out timing that coincides with the transfer start timing at which image transfer onto the sheet begins at the image transfer position, thereby sending the sheet to the image transfer position.

[0003] The image forming apparatus is also provided with a sheet transport device that transports sheets from the sheet storage section toward the registration roller unit.

[0004] Furthermore, for example, Patent Document 1 discloses a sheet feeding device that controls the distance between the trailing edge of the previous sheet and the leading edge of the next sheet by changing the timing at which the sheet conveying speed is reduced to the sheet conveying speed at the image transfer position. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-69784 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a sheet is removed from the sheet storage unit and transported, the sheet may slip. Sheet slippage can cause delays in sheet transport. For example, if a sheet transport delay occurs during a continuous print job in which images are formed sequentially on continuously transported sheets, the sheet spacing between the preceding and following sheets varies. This reduces the productivity of the image forming apparatus, i.e., the amount of printing per unit time. Furthermore, in some cases, the spacing between the following sheets may become extremely narrow, potentially causing a sheet jam in the transport path. Furthermore, if the timing of the sheet delivery by a pair of registration rollers is accelerated in an attempt to eliminate the sheet spacing variation, sheet skew correction may be insufficient.

[0007] An object of the present invention is to provide a sheet conveying device that, when a delay occurs in a succeeding sheet following a preceding sheet that is conveyed first, can make up for the sheet delay while the succeeding sheet is being conveyed, and an image forming apparatus equipped with the sheet conveying device. [Means for solving the problem]

[0008] A sheet conveying device according to one aspect of the present invention is a sheet conveying device that sequentially conveys multiple sheets, and includes a first conveying roller that receives driving force from a first drive unit to rotate and convey the sheets, a second conveying roller that is located downstream of the first conveying roller in the sheet conveying direction and receives driving force from a second drive unit to rotate and convey the sheets, a sheet sensor that is located between the first conveying roller and the second conveying roller to detect the leading and trailing ends of the sheets, and a speed control unit that controls the sheet conveying speed by each of the first conveying roller and the second conveying roller. When the leading edge of the following second sheet is not detected at a reference point when a first elapsed amount from a first point in time when the trailing edge of the preceding first sheet is detected reaches a reference amount corresponding to a predetermined sheet spacing, the speed control unit changes the sheet transport speed by the first transport roller from an initial speed to a high speed faster than the initial speed, maintains the sheet transport speed by the second transport roller at the initial speed, determines a return timing for returning the high speed to the initial speed based on a second elapsed amount from the reference point to a second point in time when the leading edge of the second sheet is detected, and returns the sheet transport speed by the first transport roller from the high speed to the initial speed at the determined return timing.

[0009] An image forming apparatus according to another aspect of the present invention includes the sheet transporting device described above, and is configured to transfer a toner image onto a sheet transported to an image transfer position by the sheet transporting device. [Effects of the Invention]

[0010] According to the present invention, when a delay occurs in a succeeding sheet following a preceding sheet that is conveyed first, it is possible to make up for the delay of the sheet while the succeeding sheet is being conveyed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the internal configuration of the image forming apparatus. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of the vicinity of the conveying path of the image forming apparatus. [Figure 4] FIG. 4 is a block diagram showing the configuration of the image forming apparatus. [Figure 5] FIG. 5 is a graph showing the relationship between the position of each sheet and the arrival time when the sheets are continuously transported from the sheet receiving unit at a constant transport speed. [Figure 6] FIG. 6 is a graph showing the relationship between the position of each sheet and the arrival time when the conveying speed of the following sheet conveyed from the sheet receiving unit is changed. [Figure 7] FIG. 7 is a flowchart illustrating an example of a procedure for a conveying speed control process executed by the control unit of the image forming apparatus. [Figure 8] FIG. 8 is a flowchart illustrating an example of a procedure for a conveying speed adjustment process executed by the control unit of the image forming apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. The embodiment described below is merely an example of the present invention, and is not intended to limit the technical scope of the present invention.

[0013] Fig. 1 is a perspective view showing the configuration of an image forming apparatus 10 according to an embodiment of the present invention. Fig. 2 is a schematic diagram showing the internal configuration of the image forming apparatus 10. In Fig. 2, the image reading unit 12 is not shown. In the following description, a vertical direction D1 is defined based on the state in which the image forming apparatus 10 is installed and ready for use (the state in Fig. 1), a front-to-rear direction D2 is defined with the front side (front face) of the image forming apparatus 10 as the front, and a left-to-right direction D3 is defined when the image forming apparatus 10 is viewed from the front side (front face).

[0014] [Image forming apparatus 10] 1, image forming apparatus 10 is a multifunction device capable of printing images on sheets such as printing paper, and has various functions such as a print function, a copy function, a facsimile function, and a scan function. Image forming apparatus 10 is not limited to the multifunction device, and may be any device that has a print function for printing images on conveyed sheets, such as a printer, a copier, or a fax machine.

[0015] The image forming apparatus 10 includes an image reading unit 12 and an image forming unit 14. The image reading unit 12 performs image reading processing to read an image of a document, and is provided in the upper part of the image forming apparatus 10. The image forming unit 14 performs image forming processing to form a color image based on an electrophotographic method, and is provided in the lower part of the image forming apparatus 10.

[0016] A discharge space 21 is provided above the image forming unit 14. The sheet after image formation is discharged into the discharge space 21 from a sheet discharge port 15A (see FIG. 2).

[0017] Image forming unit 14 includes housing 11 as the device main body. Each component that constitutes image forming unit 14 is disposed inside housing 11. Housing 11 includes an exterior frame that covers the entire image forming unit 14, and an internal frame that supports each component that constitutes image forming unit 14.

[0018] The image forming unit 14 forms a color image on a sheet such as printing paper based on the so-called tandem system.

[0019] As shown in FIG. 2, the image forming section 14 includes a plurality of image forming units 4, an intermediate transfer unit 5, an optical scanning device 13, a secondary transfer roller 20, a fixing device 16, a sheet tray 18, a sheet storage section 27, a first feeding unit 28, an operation display section 17 (see FIG. 1), a sheet transport path 26 (hereinafter abbreviated as transport path 26), a sheet transport unit 23, a registration roller unit 60, a toner container 3, a multi-sheet transport path 70 (hereinafter abbreviated as transport path 70), a second feeding unit 80, and a control section 100 (see FIG. 4). Note that the image forming section 14 may be one in which a single image is formed on a sheet by a single image forming unit 4. In this case, the intermediate transfer unit 5 is not required.

[0020] 2, the sheet storage unit 27 is provided at the bottom of the image forming apparatus 10. The sheet storage unit 27 stores a plurality of sheets and is formed, for example, in the shape of a tray with an open top. The sheet storage unit 27 is supported by the housing 11.

[0021] The first feeding unit 28 picks up multiple sheets stacked in the sheet storage section 27 one by one and sequentially feeds the sheets toward the conveyance path 26. The first feeding unit 28 includes a pickup roller 29, a feed roller 30, and a separation roller 31. The pickup roller 29 and the feed roller 30 are provided on the upper side of the rear part of the sheet storage section 27. The separation roller 31 is provided below the feed roller 30, in contact with the roller surface of the feed roller 30. Because the separation roller 31 is provided, even if multiple sheets are picked up by the pickup roller 29, only the uppermost sheet to be fed is separated from the other sheets by the separation roller 31.

[0022] The feed roller 30 is connected to a transport motor 54 (see FIG. 4). The feed roller 30 receives a rotational driving force from the transport motor 54 to transport the sheet downstream in the transport direction D11. A drive transmission mechanism (not shown) that transmits the rotation of the feed roller 30 to the pickup roller 29 is provided between the feed roller 30 and the pickup roller 29. The pickup roller 29 and the feed roller 30 are connected via the drive transmission mechanism. When the feed roller 30 is rotated by the transport motor 54, the drive transmission mechanism also rotates the pickup roller 29 in the same direction and at the same peripheral speed as the feed roller 30.

[0023] When an instruction signal to feed a sheet in sheet storage unit 27 is input to image forming apparatus 10, feed roller 30 and pickup roller 29 are rotated by the rotational driving force of conveyance motor 54, and the sheet is fed from sheet storage unit 27 to conveyance path 26. Specifically, pickup roller 29 picks up a sheet in sheet storage unit 27 and sends the sheet downstream in the feeding direction, and when the leading edge of the sheet reaches the nip portion between feed roller 30 and separation roller 31, feed roller 30 conveys the sheet to conveyance path 26.

[0024] The conveying path 26 is a guide path that guides the sheet fed by the feeding roller 30 to the sheet discharge opening 15A. As shown in Fig. 2, the conveying path 26 curves upward from the feeding roller 30 and then extends upward, passing through the secondary transfer roller 20 and reaching the sheet discharge opening 15A.

[0025] A sheet transport unit 23 and a registration roller unit 60 are provided on the transport path 26 .

[0026] The sheet transport unit 23 transports the sheet fed to the transport path 26 by the first feeding unit 28 in a transport direction D11 toward an image transfer position P0. The image transfer position P0 is a position where the toner image on the transfer belt 5A is transferred to the sheet, and is a position where the drive roller 5B and the secondary transfer roller 20 face each other. The sheet transport unit 23 receives a rotational driving force from a transport motor 56 (see FIG. 4) to transport the sheet downstream in the transport direction D11. The configuration of the sheet transport unit 23 will be described later.

[0027] The registration roller unit 60 is disposed on the conveying path 26 upstream of the image transfer position P0 in the conveying direction D11 and downstream of the sheet conveying unit 23 in the conveying direction D11. In other words, the registration roller unit 60 is provided between the image transfer position P0 and the sheet conveying unit 23. The registration roller unit 60 corrects the inclination of the sheet that is conveyed on the conveying path 26 in a state inclined with respect to the conveying direction D11, and conveys the corrected sheet downstream in the conveying direction D11. The configuration of the registration roller unit 60 will be described later.

[0028] As shown in FIG. 2, each image forming unit 4 is provided below the intermediate transfer unit 5. Each image forming unit 4 performs an image formation process to form a toner image on the surface of the transfer belt 5A based on image data input from the outside. The multiple image forming units 4 are arranged side by side in the running direction of the transfer belt 5A (the direction indicated by arrow D10). From the front to the rear of the transfer belt 5A, a yellow image forming unit 4Y, a cyan image forming unit 4C, a magenta image forming unit 4M, and a black image forming unit 4K are arranged in a row in that order.

[0029] Each image forming unit 4 includes a photosensitive drum 41, a charging device 42, a developing device 44, a primary transfer roller 45, etc. Image forming unit 4Y forms a toner image on the surface of photosensitive drum 41 using yellow toner. Image forming unit 4C forms a toner image on the surface of photosensitive drum 41 using cyan toner, image forming unit 4M forms a toner image on the surface of photosensitive drum 41 using magenta toner, and image forming unit 4K forms a toner image on the surface of photosensitive drum 41 using black toner. The toner images on photosensitive drum 41 are developed by developing device 44.

[0030] The intermediate transfer unit 5 includes a transfer belt 5A, a drive roller 5B, and a driven roller 5C. The transfer belt 5A is a belt member onto which the toner images of each color formed on the photosensitive drum 41 of each image forming unit 4 are transferred. The transfer belt 5A is provided above the photosensitive drum 41. The transfer belt 5A is an endless circular belt. The transfer belt 5A is rotatably supported by a drive roller 5B and a driven roller 5C spaced apart in the left-right direction D3. The transfer belt 5A is supported so as to be stretched over the drive roller 5B and the driven roller 5C. As the surface of the transfer belt 5A passes between the photosensitive drum 41 and the primary transfer roller 45, the toner images from each photosensitive drum 41 are transferred onto the transfer belt 5A in order, superimposed on top of each other. The toner images transferred to the transfer belt 5A are transported to the image transfer position P0 and transferred to a sheet at the image transfer position P0.

[0031] The optical scanning device 13 irradiates the photosensitive drum 41 of each image forming unit 4 with laser light based on the input image data for each color. This forms an electrostatic latent image on each photosensitive drum 41. When image forming instructions for forming images on multiple sheets are input to the image forming device 10 along with image data corresponding to each sheet, the control unit 100 determines the scanning start timing for starting laser scanning of the photosensitive drum 41 with laser light based on the image data, and irradiates the photosensitive drum 41 with the laser light at the scanning start timing determined for each of the multiple sheets.

[0032] The secondary transfer roller 20 is disposed opposite the drive roller 5B across the vertically extending transport path 26. The secondary transfer roller 20 performs a transfer process in which the toner image on the transfer belt 5A is transferred to a sheet by a transfer potential applied to the secondary transfer roller 20. The position at which the toner image is transferred to the sheet by the secondary transfer roller 20 is the image transfer position P0. The sheet to which the toner image has been transferred is transported to the fixing device 16.

[0033] The fixing device 16 heats the toner image transferred to the sheet to fix it to the sheet, and includes a heating roller 16A and a pressure roller 16B. The sheet transported to the fixing device 16 is conveyed while being sandwiched between the heating roller 16A and the pressure roller 16B. During this conveyance, heat is transferred from the heating roller 16A to the toner image transferred to the sheet, heating the toner image. This fixes the toner image to the sheet.

[0034] The sheet on which the image has been formed and which has passed through the fixing device 16 is discharged from the sheet discharge port 15A onto the sheet tray 18 by a discharge roller 24 provided at the most downstream end of the conveying path 26.

[0035] As shown in FIG. 2, a conveying path 70 is provided between the optical scanning device 13 and the sheet storage section 27. The conveying path 70 is a guide path that guides sheets fed by a second feeding unit 80 (described later) to the conveying path 26. The conveying path 70 is formed by an upper guide member 71 and a lower guide member 72 that extend in the front-rear direction D2. The upper guide member 71 and the lower guide member 72 are arranged at a predetermined distance so as to face each other in the up-down direction 6. The space sandwiched between the upper guide member 71 and the lower guide member 72 forms the conveying path 70. The conveying path 70 extends in the front-rear direction D2 of the image forming unit 14, and is connected to the conveying path 26 at a connection point P3 (see FIG. 3) on the rear side of the image forming unit 14.

[0036] A manual sheet receiving section 11A is provided on the front side of the image forming section 14. The sheet receiving section 11A also serves as a front cover of the housing 11 of the image forming section 14.

[0037] The sheet receiving section 11A is configured so that the entrance to the conveying path 70 can be opened and closed relative to the front surface of the housing 11. Figure 2 shows the sheet receiving section 11A in a state where it is closed relative to the front surface of the housing 11. When the sheet receiving section 11A is opened relative to the front surface of the housing 11 and its inner surface faces upward, multiple sheets of any size can be placed on the inner surface.

[0038] A second feeding unit 80 is provided near the entrance on the front side of the conveying path 70. The second feeding unit 80 picks up multiple sheets placed on the sheet receiving section 11A one by one and sequentially feeds the sheets toward the conveying path 70. The second feeding unit 80 includes a pickup roller 81, a feeding roller 82, and a driven roller 83.

[0039] The feed roller 82 is connected to the transport motor 55 (see FIG. 4). The feed roller 82 receives a rotational driving force from the transport motor 55 to transport the sheet downstream in the transport direction D12. A drive transmission mechanism (not shown) that transmits the rotation of the feed roller 82 to the pickup roller 81 is provided between the feed roller 82 and the pickup roller 81. The pickup roller 81 and the feed roller 82 are connected via the drive transmission mechanism. When the feed roller 82 is rotated by the transport motor 55, the pickup roller 81 also rotates in the same direction as the feed roller 82 due to the drive transmission mechanism.

[0040] When an instruction signal to feed a sheet in sheet receiving unit 11A is input to image forming apparatus 10, feed roller 82 and pickup roller 81 are rotated by the rotational driving force of conveyance motor 55, and the sheet is fed from sheet receiving unit 11A to conveyance path 70. Specifically, pickup roller 81 picks up the sheet in sheet receiving unit 11A and sends the sheet downstream in conveyance direction D12, and when the leading edge of the sheet reaches the nip portion between feed roller 82 and driven roller 83, feed roller 82 conveys the sheet to conveyance path 70.

[0041] A first conveying roller pair 91 and a second conveying roller pair 92 are provided on the conveying path 70. The first conveying roller pair 91 and the second conveying roller pair 92 convey the sheet fed to the conveying path 70 by the second feeding unit 80 in the conveying direction D12, and convey the sheet to the conveying path 26. The configurations of the first conveying roller pair 91 and the second conveying roller pair 92 will be described later.

[0042] When images are formed on both sides of a sheet in the image forming unit 14, the sheet with an image formed on one side that has passed through the fixing device 16 is inverted and then transported again upstream of the secondary transfer roller 20. Specifically, the discharge rollers 24 are stopped in a state where the leading edge of the sheet with an image formed on one side is exposed to the outside through the sheet discharge opening 15A. At this time, the trailing edge of the sheet is held in a state where it is clamped by the discharge rollers 24. Thereafter, the discharge rollers 24 are driven in the reverse direction, causing the sheet to switch back and be fed backward.

[0043] As shown in FIG. 2, the image forming unit 14 includes a reverse conveyance path 25 that branches off from a branch point P1 on the conveyance path 26 downstream of the fixing device 16 and connects to a junction point P2 on the conveyance path 26. The junction point P2 is located upstream of the sheet conveyance unit 23 on the conveyance path 26. A sheet conveyed in reverse from the sheet discharge port 15A is guided to the reverse conveyance path 25, conveyed by conveyance rollers 25A provided on the reverse conveyance path 25, passes through the reverse conveyance path 25, merges with the conveyance path 26, and is conveyed again to the secondary transfer roller 20. When the sheet then reaches the secondary transfer roller 20, a toner image is transferred onto the back surface of the sheet, and the sheet passes through the fixing device 16, forming an image on the back surface of the sheet. The sheet with images formed on both sides is discharged from the sheet discharge port 15A to the sheet tray 18 by the discharge rollers 24, which are driven back to normal rotation.

[0044] [Sheet transport unit 23] 3, the sheet transport unit 23 has a transport roller 23A that is rotationally driven by a driving force from a transport motor 56 (see FIG. 4), and a driven roller 23B that is disposed in contact with the outer circumferential surface of the transport roller 23A. The driving force from the transport motor 56 is transmitted to a rotation shaft 47 of the transport roller 23A. The transport roller 23A and the driven roller 23B form a transport roller pair.

[0045] Rotation shaft 49 of driven roller 23B is biased by spring 23C with a predetermined elastic force (spring force) toward transport roller 23A, so that driven roller 23B is pressed against transport roller 23A. When transport roller 23A is rotationally driven in this state, driven roller 23B is driven.

[0046] A rotation shaft 49 of the driven roller 23B is supported by a support portion 48 provided on a guide member or the like of the transport path 26. In this embodiment, the driven roller 23B is supported by the support portion 48 so as to be movable between a contact position where it contacts the transport roller 23A and a contact release position where it is separated from the transport roller 23A.

[0047] 4 is a block diagram showing the configuration of the image forming apparatus 10. A solenoid 46 is provided inside the housing 11. The solenoid 46 is connected to the control unit 100 and is activated when power is supplied by the control unit 100. The plunger of the solenoid 46 is connected to the support portion 48 via a link member (not shown). When power is supplied to the solenoid 46, the plunger is actuated to move the support portion 48 from the contact position to the contact release position. When power is removed from the solenoid 46, the plunger is returned to its original position by a tension spring provided in the solenoid 46, and the support portion 48 is returned to the contact position by the spring force of the spring 23C.

[0048] 3, sheet detection sensors 52 and 53 are provided in the conveying path 26. The sheet detection sensors 52 and 53 detect the leading or trailing edge of the sheet being conveyed. The sheet detection sensors 52 and 53 are provided near the center of the conveying path 26 in the width direction.

[0049] The sheet detection sensor 52 is provided on the conveying path 26 upstream of the sheet conveying unit 23 in the conveying direction D11 and downstream of a junction P3 between the conveying path 70 and the conveying path 26. In other words, the sheet detection sensor 52 is provided between the sheet conveying unit 23 and the junction P3. In this embodiment, the sheet detection sensor 52 is provided at a position close to the sheet conveying unit 23.

[0050] The sheet detection sensor 53 is provided in the conveying path 26 upstream of the registration roller unit 60 in the conveying direction D11 and downstream of the sheet conveying unit 23. In other words, the sheet detection sensor 53 is provided between the registration roller unit 60 and the sheet conveying unit 23. In this embodiment, the sheet detection sensor 53 is provided at a position close to the registration roller unit 60.

[0051] [Registration Roller Unit 60] 3, the registration roller unit 60 is provided in the conveying path 26. The registration roller unit 60 is provided in the conveying path 26 upstream of the image transfer position P0 in the conveying direction D11 and downstream of the sheet detection sensor 53 in the conveying direction D11.

[0052] The registration roller unit 60 corrects the inclination (transport deviation) of the sheet that is transported by the sheet transport unit 23 in an inclined state with respect to the transport direction D11, and transports the corrected sheet to the image transfer position P0 at a predetermined timing.

[0053] As shown in Fig. 3, the registration roller unit 60 has a registration roller 60A that is driven to rotate by a driving force from a transport motor 57 (see Fig. 4), and a driven roller 60B that is disposed in contact with the outer circumferential surface of the registration roller 60A. The driving force from the transport motor 57 is transmitted to the rotation shaft of the registration roller 60A. The registration roller 60A and the driven roller 60B form a transport roller pair.

[0054] The driven roller 60B is biased toward the registration roller 60A by the spring 60C. As a result, the driven roller 60B is pressed against the registration roller 60A. When the registration roller 60A is rotated in this state, the driven roller 60B is driven.

[0055] [First conveyor roller pair 91] In the conveyance path 70, the first conveyance roller pair 91 is provided downstream of the second feeding unit 80 in the conveyance direction D12. The first conveyance roller pair 91 includes an upstream conveyance roller 91A (an example of a first conveyance roller of the present invention) that is driven to rotate by a driving force from a conveyance motor 58 (an example of a first drive unit of the present invention, see FIG. 4), and a driven roller 91B that is disposed in contact with the outer circumferential surface of the upstream conveyance roller 91A. The driving force from the conveyance motor 58 is transmitted to the rotation shaft of the upstream conveyance roller 91A. The driven roller 91B is biased toward the upstream conveyance roller 91A by, for example, a spring (not shown).

[0056] [Second conveying roller pair 92] In the conveyance path 70, the second conveyance roller pair 92 is disposed downstream of the first conveyance roller pair 91 in the conveyance direction D12 and upstream of the connecting point P3 in the conveyance direction D12. The second conveyance roller pair 92 includes a downstream conveyance roller 92A (an example of a second conveyance roller of the present invention) that is driven to rotate by a driving force from a conveyance motor 59 (an example of a second drive unit of the present invention; see FIG. 4), and a driven roller 92B that is disposed in contact with the outer circumferential surface of the downstream conveyance roller 92A. The driving force from the conveyance motor 59 is transmitted to the rotation shaft of the downstream conveyance roller 92A. The driven roller 92B is biased toward the downstream conveyance roller 92A by, for example, a spring (not shown).

[0057] As shown in FIG. 3, a sheet detection sensor 51 is provided in the conveying path 70. The sheet detection sensor 51 detects the leading edge or trailing edge of a sheet being conveyed. The sheet detection sensor 51 is provided near the center of the conveying path 70 in the width direction. The sheet detection sensor 51 is provided in the conveying path 70 downstream of the first conveying roller pair 91 in the conveying direction D12 and upstream of the second conveying roller pair 92. In other words, the sheet detection sensor 51 is provided between the first conveying roller pair 91 and the second conveying roller pair 92, and in this embodiment, for example, is provided at approximately the midpoint between the first conveying roller pair 91 and the second conveying roller pair 92.

[0058] The sheet detection sensors 51 to 53 are, for example, reflective optical sensors. The sheet detection sensors 51 to 53 are each connected to the control unit 100, and their detection signals are sent to the control unit 100. The control unit 100 detects the leading or trailing edge of the conveyed sheet based on changes in the detection signals sent from the sheet detection sensors 51 to 53. Note that such detection methods are conventionally known, and therefore a detailed description thereof will be omitted.

[0059] The conveying motors 55 to 59 are, for example, stepping motors or inner brushless motors. These motors have high speed response and high positional accuracy, but require a certain waiting time after stopping before they can be driven again.

[0060] [Control unit 100] The control unit 100 performs overall control of the image forming apparatus 10, controls the rotational driving of each roller provided in the conveying paths 26 and 70, and also controls the sheet conveying speed by each roller.

[0061] 4, the control unit 100 is composed of a CPU 101, a ROM 102, a RAM 103, a storage unit 104, etc. The control unit 100 is electrically connected to the motors 54 to 59, the sheet detection sensors 51 to 53, the solenoid 46, etc. via signal lines, etc. The motors 54 to 59 are connected to the control unit 100, and are individually driven and controlled by receiving individual control signals from the control unit 100.

[0062] The CPU 101 is a processor that executes computer programs to perform various data processing and predetermined control. The RAM 103 is a computer-readable volatile or nonvolatile storage device. The RAM 103 temporarily stores the computer programs executed by the CPU 101 and data output or referenced by the CPU 101 during the execution of various processes. The ROM 102 is a nonvolatile storage device that pre-stores control programs such as a BIOS and an OS that cause the CPU 101 to execute various arithmetic processes. The storage unit 104 is a flash memory that stores various information. The storage unit 104 stores control programs for executing various processes by the control unit 100, as well as data, thresholds, reference values, and the like used in the various processes. The storage unit 104 may also be a nonvolatile storage device such as an HDD or SSD connected directly to the control unit 100 or indirectly via the Internet.

[0063] In image forming apparatus 10, when a sheet is picked up from sheet receiving section 11A or sheet storage section 27 and fed, the sheet may slip on the pickup roller or feed roller. Sheet slippage can cause delays in sheet transport. For example, if a sheet transport delay occurs during a continuous print job in which images are sequentially formed on continuously fed sheets, the sheet spacing between the preceding sheet (first sheet) and the following sheet (second sheet) varies. This reduces the productivity of image forming apparatus 10, i.e., the number of sheets printed per unit time. Furthermore, in some cases, the spacing between the next sheet may become extremely narrow, potentially causing a sheet jam in transport path 26 or transport path 70. Furthermore, if the timing of sheet feed by registration roller 60A is accelerated to eliminate the sheet spacing variation, sheet skew correction may be insufficient.

[0064] In this embodiment, the control unit 100 controls the speed of the sheet being transported as described below, so that even if a delay occurs in the following sheet following the preceding sheet that is transported first, it is possible to make up for the delay in the sheet while the next sheet is being transported.

[0065] The control unit 100 controls the sheet conveying speed of the sheet being conveyed from the sheet receiving unit 11A or the sheet storage unit 27 toward the image transfer position P0 by the CPU 101 executing various control programs pre-stored in the ROM 102 or the memory unit 104.

[0066] 4, the control unit 100 includes various processing units such as a registration control unit 105 and a conveying speed control unit 106. Note that in this embodiment, not all of these processing units are necessarily required, and some may be omitted.

[0067] The control unit 100 functions as various processing units such as a registration control unit 105 and a conveyance speed control unit 106 by the CPU 101 executing various arithmetic processes in accordance with the control program. The control unit 100 or the CPU 101 is an example of a computer or processor that executes the control program. Note that some or all of the processing units included in the control unit 100 may be configured with electronic circuits such as a motor driver. The control program may also be a program that causes multiple processors to function as the various processing units.

[0068] The registration control unit 105 controls the rotational drive of the registration roller 60A so that the sheet is transported by the sheet transport unit 23 while the registration roller 60A of the registration roller unit 60 is stopped, and the sheet whose leading edge has reached the nip portion between the registration roller 60A and the driven roller 60B is bent, and then the sheet is sent out at a predetermined sending timing that coincides with the transfer start timing at which the transfer of the toner image onto the sheet begins at the image transfer position P0.

[0069] The conveying speed control unit 106 controls the rotational drive of the upstream conveying roller 91A and the downstream conveying roller 92A for the sheet conveyed from the sheet receiving unit 11A, thereby controlling the conveying speed of the sheet conveyed along the conveying path 70. The conveying speed control unit 106 is an example of the speed control unit of the present invention.

[0070] 5 and 6 are graphs showing the relationship between the position of each sheet and the arrival time when sheets are continuously conveyed from the sheet receiving section 11A. In each diagram, the horizontal axis represents the position in the conveying direction, and the vertical axis represents time. In each diagram, line L11 shown by a solid line represents the relationship between the position of the leading edge of the preceding sheet (first sheet) and the arrival time, and line L12 shown by a dashed line represents the relationship between the position of the trailing edge of the preceding sheet and the arrival time. Line L12 shown by a solid line represents the relationship between the position of the leading edge of the following sheet (second sheet) and the arrival time.

[0071] 5 is a graph showing the case where both the preceding sheet and the following sheet are conveyed normally at the initial speed V1 without slipping. In FIG. 5, the dashed two-dot line L22 indicates the position and arrival time of the leading edge of the following sheet when the following sheet is fed with a delay of X (ms) (=Δt) due to, for example, slippage.

[0072] 5, when the preceding sheet is conveyed normally, feeding of the preceding sheet begins at time T0, the timing when the leading edge of the preceding sheet is detected by sheet detection sensor 51 at position P1 is time T1, and the timing when the trailing edge of the preceding sheet is detected by sheet detection sensor 51 is time T3, which is later than time T2. Furthermore, feeding of the following sheet begins at time T2, which is earlier than time T3, with a predetermined set distance Ds1 between it and the preceding sheet, and the timing when the leading edge of the following sheet is detected by sheet detection sensor 51 at position P1 is time T4, which is later than time T3.

[0073] For example, consider a case where a following sheet is fed at time T21, which is delayed by delay time X (ms) from time T2. Hereinafter, a following sheet that is fed with a delay of delay time X may be referred to as a delayed sheet.

[0074] In this case, if conveyance continues at the initial speed V1, the leading edge of the delayed sheet follows line L22. Until the leading edge of the delayed sheet reaches position P1, it is unclear whether the delayed sheet is delayed. However, once the leading edge of the delayed sheet reaches position P1 and is detected by the sheet detection sensor 51, the time difference Δt1 (= T41 - T3) between time T3 when the trailing edge of the preceding sheet is detected and time T41 when the leading edge of the delayed sheet is detected is obtained. If this time difference Δt1 is longer than the time difference Δt0 (= T4 - T3) when no delay occurs, it is determined that a delay has occurred, and the delay time (= Δt1 - Δt0) can be calculated. Furthermore, the actual sheet interval Ds2 can be calculated from the time difference Δt1 and the initial speed V1, and the delay amount ΔD (= Ds2 - Ds1), which indicates the degree of delay, can be calculated.

[0075] In this case, after the leading edge of the delayed sheet is detected (after time T4), the sheet conveying speed (circumferential speed) by the upstream conveying roller 91A can be increased to make up for the delay, and then the sheet conveying speed by the upstream conveying roller 91A can be returned to the original initial speed V1.

[0076] However, with this speed control, if the delay amount ΔD is relatively large, the upstream transport roller 91A must be rapidly accelerated and then rapidly decelerated in order to make up for the delay before the leading edge of the delayed sheet reaches the second transport roller pair 92. This causes the transport speed to overshoot or undershoot, resulting in an unstable sheet transport speed. Furthermore, the sudden speed change may cause damage to the sheet. On the other hand, if priority is given to sheet transport stability and preventing sheet damage, the delay cannot be made up for before the leading edge of the delayed sheet reaches the second transport roller pair 92.

[0077] In contrast, in this embodiment, as shown by line L23 in FIG. 6, when the sheet detection sensor 51 detects the trailing edge of a preceding sheet (first sheet of the present invention) being conveyed first at position P1, the conveying speed control unit 106 measures a first elapsed time Ta (first elapsed amount of the present invention) from that time T3 (first time point of the present invention). Then, when the count value of the first elapsed time Ta reaches a reference time (reference amount of the present invention) required to convey a sheet at the set interval Ds1 at the initial speed V1, the conveying speed control unit 106 determines whether the leading edge of a subsequent following sheet (second sheet of the present invention) has been detected at that time point (hereinafter referred to as the reference time point). Then, if the leading edge of the following sheet has not been detected at the reference time point, the conveying speed control unit 106 changes the conveying speed of the following sheet by the upstream conveying rollers 91A from the initial speed V1 to a high speed V2 that is faster than the initial speed V1. At this time, the conveying speed control unit 106 maintains the sheet conveying speed by the downstream conveying rollers 92A at the initial speed V1.

[0078] 6 shows a line L23 indicating the position and arrival time of the leading edge of the following sheet when the conveying speed control unit 106 changes the conveying speed of the following sheet due to a delay in feeding.

[0079] As a result, when a delay in conveyance of the following sheet occurs, the sheet conveyance speed by the upstream conveyance roller 91A is changed to the high speed V2 before the leading edge of the following sheet is detected.

[0080] Here, the reference time is the time Δt0 (=T4-T3) required to transport the sheet at the set interval Ds1 at the initial speed V1, and therefore the calculation processing time for the speed change by the transport speed control unit 106 is extremely short and can be ignored. Therefore, the reference time can essentially be regarded as the time T4 shown in Figure 6, that is, the time T4 at which the trailing end of the following sheet would be detected by the sheet detection sensor 50 if no delay occurred.

[0081] In addition, the conveying speed control unit 106 determines the return timing (time T42) for returning the high speed V2 to the initial speed V1 based on a second elapsed time Tb (second elapsed amount according to the present invention) from the reference time point to time T40 (second time point according to the present invention) when the leading edge of the following sheet is actually detected.

[0082] Specifically, if the estimated duration (estimated duration of the present invention) for continuing conveyance at the high speed V2 after the reference time point is Z, the conveyance speed control unit 106 determines the return timing to be the point in time obtained by adding the estimated duration Z to the reference time point (time point T4).

[0083] Here, the distance (=V2·Z) when the sheet is conveyed at the high speed V2 for the estimated duration Z is equivalent to the distance (=V1(X+Z)) when the sheet is conveyed at the initial speed V1 for the delay time X (ms) and then further conveyed for the estimated duration Z, and therefore the following relational expression (1) holds.

[0084] V2 Z=V1(X+Z) (1)

[0085] Furthermore, since the distance traveled when the sheet is transported at the high speed V2 for the second elapsed time Tb is equivalent to the distance traveled when the sheet is transported at the initial speed V1 for the delay time X (ms), the following relational expression (2) holds:

[0086] V2 Tb = V1 X X=V2 Tb / V1 (2)

[0087] Here, by substituting the above formula (2) into the above formula (1) and rearranging the estimated duration Z, the following calculation formula can be derived.

[0088] Z=V2 Tb / (V2-V1) (3)

[0089] In a situation where the leading edge of the delayed sheet is not actually detected, the second elapsed time Tb is an unknown quantity, and therefore the calculation formula (3) is a linear function with the second elapsed time Tb as a variable. In this embodiment, the conveying speed control unit 106 calculates the estimated duration Z using the second elapsed time Tb and the calculation formula (3) at time T40 when the leading edge of the delayed sheet is actually detected by the sheet detection sensor 51, and determines time T42, which is obtained by adding the estimated duration Z to the reference time point (time point T4), as the return timing.

[0090] Then, when the conveying speed control unit 106 determines that the elapsed time from the reference time point (time point T4) has reached the return timing (time point T42), it returns the sheet conveying speed by the upstream conveying roller 91A from the high speed V2 to the initial speed V1.

[0091] As a result, as shown in FIG. 6, at time T42, the leading edge position P2 of the delayed sheet coincides with the leading edge position of the following sheet if there was no delay, and the delay of the following sheet is made up.

[0092] In this way, the sheet transport speed is adjusted by the upstream transport roller 91A, so that the delayed sheet can be made up for by the time it reaches the second transport roller pair 92 without a sudden acceleration or deceleration of the upstream transport roller 91A.

[0093] If the leading edge of the following sheet is detected by the sheet detection sensor 51 before the first elapsed time Ta reaches the reference time, this means that the following sheet is being transported earlier than the reference time due to misalignment during feeding, double feeding, etc. In this case, the transport speed control unit 106 changes the transport speed of the following sheet by the upstream transport roller 91A from the initial speed V1 to a lower speed V3 that is slower than the initial speed V1, and returns the speed to the original initial speed V1 after the following sheet has been transported at the lower speed V3 for a time or distance corresponding to the earlier transport.

[0094] [Transport speed control processing] 7 and 8, an example of the procedure of the conveying speed control process executed by the control unit 100 will be described, along with a description of the conveying speed control method of the present invention. In each figure, S11, S12, ... indicate the numbers (step numbers) of the processing procedures.

[0095] Note that one or more steps included in the conveying speed control process described below may be omitted as appropriate. Furthermore, the steps in the conveying speed control process may be executed in a different order as long as the same operational effect is achieved. Furthermore, the following description will be given using an example in which one processor corresponding to the control unit 100 executes the processing of each step in the conveying speed control process, but the steps in the conveying speed control process may be executed in a distributed manner by multiple processors.

[0096] The conveying speed control process described below is executed when a continuous print job is input in which sheets in the sheet receiving unit 11A are continuously conveyed and images are printed on the sheets.

[0097] 7, in step S11, the control unit 100 drives the second feeding unit 80 to start feeding the first sheet (hereinafter referred to as the preceding sheet) from the sheet receiving unit 11A. Then, in step S12, the control unit 100 drives the upstream transport roller 91A and the downstream transport roller 92A to rotate, thereby transporting the preceding sheet at an initial speed V1.

[0098] In step S13, the control unit 100 determines whether the leading edge of the first preceding sheet has been detected by the sheet detection sensor 51. If the leading edge of the preceding sheet has not been detected and a predetermined time has elapsed in this state, a timeout occurs, and the control unit 100 determines that a sheet conveyance error has occurred (S14). In this case, the control unit 100 interrupts the process, performs error processing to output an error message (S15), and then ends the series of processes.

[0099] On the other hand, when the leading edge of the preceding sheet is detected by the sheet detection sensor 51, the control unit 100 starts feeding the next sheet (hereinafter referred to as the following sheet) when the sheet interval of the set interval Ds1 is secured between the leading edge of the preceding sheet and the sheet (S17). Note that when the leading edge of the preceding sheet is detected, the control unit 100 conveys the sheet a specified distance that is the remaining length to the trailing edge plus the set interval Ds1, and starts feeding the following sheet at the timing when the preceding sheet has been conveyed by the specified amount.

[0100] In the next step S18, a conveying speed adjustment process is performed to adjust the conveying speed of the upstream conveying rollers 91A.

[0101] Specifically, as shown in FIG. 8, the control unit 100 determines whether the first elapsed time Ta from the time T3 at which the trailing end of the preceding sheet is detected reaches the reference time before the leading end of the following sheet is detected by the sheet detection sensor 51 (S181).

[0102] In step S181, if it is determined that the first elapsed time Ta has reached the reference time before the leading edge of the following sheet is detected, it means that there is a delay in the conveyance of the following sheet. In this case, the control unit 100 increases the conveyance speed of the following sheet by the upstream conveyance roller 91A from the initial speed V1 to the high speed V2 (S182).

[0103] Then, after the leading edge of the following seat is detected, the control unit 100 calculates the estimated duration Z using the calculation formula (3) and determines the return timing to be the point in time obtained by adding the estimated duration Z to the reference point in time (point in time T4) (S183).

[0104] Then, when the control unit 100 determines that the elapsed time from the reference time point (time point T4) has reached the return timing (time point T42) (S184), it returns the sheet conveying speed by the upstream conveying roller 91A from the high speed V2 to the initial speed V1 (S185).

[0105] On the other hand, if it is determined in step S181 that the first elapsed time Ta has not reached the reference time before the leading edge of the following sheet is detected, the control unit 100 determines in the next step S186 whether the leading edge of the following sheet is detected before the first elapsed time Ta reaches the reference time (S186). If the leading edge of the following sheet is detected before the first elapsed time Ta reaches the reference time, this means that the following sheet is being transported earlier than normal due to misalignment during feeding, double feeding, or the like. In this case, the control unit 100 slows the transport speed of the following sheet by the upstream transport roller 91A from the initial speed V1 to a low speed V3 that is slower than the initial speed V1 (S187). Note that the following sheet may be temporarily stopped by the amount of its earlier arrival without slowing down the transport speed.

[0106] Thereafter, the control unit 100 calculates the sheet interval at the time when the leading edge of the following sheet is detected based on the initial speed V1 and the time difference from the rear end of the preceding sheet to the detection of the leading edge of the following sheet, and calculates the time required for the calculated sheet interval to reach the set interval Ds1 based on the low speed V3.Then, the control unit 100 determines the time when the leading edge of the following sheet is detected plus the required time as the return timing (S188).

[0107] Then, when the control unit 100 determines that the elapsed time since the leading edge of the following sheet was detected has reached the return timing (S189), it returns the sheet conveying speed by the upstream conveying roller 91A from the low speed V3 to the initial speed V1 (S185).

[0108] In addition, in step S186, if it is determined that the leading edge of the following sheet has not been detected before the first elapsed time Ta reaches the reference time, that is, if the timing when the first elapsed time Ta reaches the reference time and the timing when the leading edge of the following sheet is detected are approximately simultaneous, there is no delay in the following sheet, there is no early transport, and the sheet is transported at an appropriate sheet interval, so in this case, the transport speed by the upstream transport roller 91A is not adjusted and is maintained at the initial speed V1.

[0109] 7, the control unit 100 determines whether the following sheet is the last sheet, and if it is not the last sheet, returns to step S17 and repeats the processing from step S17 onwards. If the following sheet is the last sheet, the series of processing ends.

[0110] As described above, in this embodiment, because the above-described conveying speed control process is performed, even if the following sheet is delayed, the delay of the following sheet can be made up for by the time the following sheet reaches the downstream second conveying roller pair 92 without abrupt acceleration or deceleration of the upstream conveying roller 91A, and the sheet interval can be adjusted to the set interval Ds1. Furthermore, if the following sheet is conveyed early, the following sheet is temporarily decelerated, and in this case as well, the sheet interval can be adjusted to the set interval Ds1.

[0111] In the above embodiment, an example of feeding sheets from the sheet receiving section 11A has been illustrated, but when feeding sheets continuously from the sheet storage section 27, a similar conveying speed control process can be applied to the conveying roller 23A of the sheet conveying unit 23.

[0112] Furthermore, in the above-described embodiment, an example was described in which elapsed time was used as the first elapsed amount and the second elapsed amount of the present invention. However, for example, if the transport motors 58, 59 are motors that are driven by applying pulse signals like stepping motors, and whose rotation angle (number of rotations) is proportional to the number of pulse signals (number of steps), the number of steps for the transport motors 58, 59 may be applied instead of the elapsed time.

[0113] In addition, in the above-described embodiment, image forming apparatus 10 was exemplified as an example of an image forming apparatus of the present invention, but the present invention can also be understood as a sheet conveying device equipped with upstream conveying rollers 91A, downstream conveying rollers 92A, and a control unit 100. [Explanation of symbols]

[0114] 10: Image forming device 11A: Seat receiving part 14: Image forming unit 23: Sheet transport unit 23A: Transport roller 23B: Driven roller 26: Sheet transport path 27: Sheet storage area 28: First feeding unit 29: Pickup roller 30: Feed roller 50-53: Sheet detection sensor 54-59: Motor 60: Registration roller unit 70: Multi-sheet transport path 80: Second feeding unit 81: Pickup roller 82: Feeding roller 91: First conveying roller pair 91A: Upstream transport roller 91B: Driven roller 92: Second conveying roller pair 92A: Downstream transport roller 92B: Driven roller 105: Resist control unit 106: Conveying speed control section

Claims

1. A sheet conveying device that sequentially conveys a plurality of sheets, a first conveying roller that receives a driving force from a first driving unit and is driven to rotate to convey the sheet; a second transport roller provided downstream of the first transport roller in a sheet transport direction, the second transport roller being rotationally driven by a driving force from a second drive unit to transport the sheet; a sheet sensor provided between the first conveying roller and the second conveying roller, the sheet sensor detecting the leading edge and the trailing edge of the sheet; a speed control unit that controls a sheet conveying speed by each of the first conveying roller and the second conveying roller; Equipped with The speed control unit when the leading edge of the following second sheet is not detected at a reference time when a first elapsed amount from a first time when the trailing edge of the preceding first sheet is detected reaches a reference amount corresponding to a predetermined sheet interval, the sheet conveyance speed by the first conveyance roller is changed from an initial speed to a high speed that is faster than the initial speed, and the sheet conveyance speed by the second conveyance roller is maintained at the initial speed; determining a return timing for returning the high speed to the initial speed based on a second elapsed amount from the reference time point to a second time point at which the leading edge of the second sheet is detected; The sheet conveying device returns the sheet conveying speed by the first conveying roller from the high speed to the initial speed at the determined return timing.

2. The speed control unit 2. The sheet conveying device according to claim 1, wherein when the initial speed is V1, the high speed is V2, and the second elapsed amount is Tb, an estimated continuation amount Z from the reference point is calculated using the following calculation formula, and the point at which the estimated continuation amount Z is added to the reference point is determined as the return timing. Z=V2・Tb / (V2-V1)

3. The sheet conveying device according to claim 1 or 2, an image forming apparatus that transfers a toner image onto a sheet that is transported to an image transfer position by the sheet transport device;

Images