Image forming apparatus and control method

Abstract

To make it possible to continue appropriate processing even if sheet detection means has already detected a sheet at the time when it is time to feed the next sheet in an image forming device.SOLUTION: An image forming apparatus 1 includes: a sheet feeding roller 13 that feeds a sheet 11 toward a sheet conveyance path 14; a sheet feeding sensor 18 that is located downstream of the sheet feeding roller 13 and detects the sheet 11; and a controller 9 that re-sets the sheet-feeding timing to a predetermined time-delayed timing when the sheet feeding sensor 18 has already detected a sheet at a timing of feeding the sheet 11 by the sheet feeding roller 13.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and a control method, and more particularly to an image forming apparatus capable of continuously feeding sheets such as printing paper and forming images thereon, and a control method thereof. [Background technology]

[0002] Conventionally, in an image forming apparatus capable of continuously feeding sheets such as printing paper, a sensor is provided at a predetermined position between a feed roller and a timing roller, and the sensor detects the sheet interval between the preceding sheet and the succeeding sheet (for example, Patent Document 1). In this conventional apparatus, when the sheet interval between the preceding sheet and the succeeding sheet becomes smaller than a predetermined value, it becomes difficult to detect the sheet interval, so the sheet feed timing of the succeeding sheet is delayed by a predetermined amount so that the sheet interval can be detected steadily. Therefore, the conventional apparatus can adjust the sheet feed timing of the succeeding sheet based on the sheet interval detected by the sensor so that the sheet interval between the preceding sheet and the succeeding sheet is constant.

[0003] For example, if the next sheet is fed together with the previous sheet during feeding of the previous sheet, the next sheet stops at a position that has advanced a certain distance downstream. In this state, when the feeding operation of the next sheet is started, the timing at which the next sheet reaches the sensor is earlier than usual. Therefore, when the sensor detects the next sheet earlier than usual, the image forming device performs control to temporarily suspend the feeding operation of the next sheet, thereby widening the sheet interval with the previous sheet. Thereafter, the image forming device resumes the feeding operation of the next sheet when the sheet interval with the previous sheet becomes a predetermined interval, thereby enabling continuous feeding of the next sheet following the previous sheet.

[0004] Incidentally, the above-mentioned sensor may be provided at a position relatively close to the paper feed roller between the paper feed roller and the timing roller. In this case, when the previous sheet is fed, if the next sheet is fed further downstream beyond the position of the paper feed roller, the leading edge of the next sheet may reach the detection position of the sensor. When this phenomenon occurs, even if the trailing edge of the previous sheet passes through the detection position of the sensor, the leading edge of the next sheet has reached the detection position of the sensor, so the sensor continues to detect the sheet (for example, the ON state). Therefore, since the sensor has already detected the sheet when it is time to feed the next sheet, the image forming apparatus cannot detect the leading edge of the next sheet after starting the feeding operation of the next sheet. In such a case, the image forming apparatus erroneously detects that the sheet interval is narrowed and a jam has occurred, and immediately interrupts the execution of the job. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-118886 A Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the present invention has been made to solve the above-mentioned problems, and aims to provide an image forming apparatus and a control method thereof that are capable of continuing appropriate processing even if the sheet detection means has already detected a sheet when it is time to feed the next sheet.

[0007] In order to achieve the above object, the invention according to claim 1 is an image forming apparatus comprising: a sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means for detecting a sheet; and a sheet feeding control means for resetting the sheet feeding timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at a timing for feeding the sheet by the sheet feeding means, the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The paper feed control means During a period from when the sheet feed timing is reset to when the sheet feed timing is reset, the sheet feed means is not caused to perform a sheet feed operation; This configuration is characterized in that it is determined whether or not to cause the paper feeding means to perform a sheet feeding operation at the reset paper feeding timing, depending on the detection result of the sheet detection means during the period from when the paper feeding timing is reset to when the reset paper feeding timing occurs. The invention according to claim 2 is an image forming apparatus comprising: a sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means for detecting a sheet; and a sheet feeding control means for resetting the sheet feeding timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at a timing for feeding the sheet by the sheet feeding means; the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The paper feed control means During a period from when the sheet feed timing is reset to when the sheet feed timing is reset, the sheet feed means is not caused to perform a sheet feed operation; This configuration is characterized in that if the sheet detection means continues to detect a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs, the sheet feed operation by the paper feed means is started at the reset paper feed timing. The invention according to claim 3 is an image forming apparatus comprising: a sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means for detecting a sheet; and a sheet feeding control means for resetting the sheet feeding timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at a timing for feeding the sheet by the sheet feeding means, the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The paper feed control means During a period from when the sheet feed timing is reset to when the sheet feed timing is reset, the sheet feed means is not caused to perform a sheet feed operation;This configuration is characterized in that if the sheet detection means changes to a state in which it does not detect a sheet during the period from when the sheet feed timing is reset to when the reset sheet feed timing occurs, the sheet feed means is not caused to perform a sheet feed operation.

[0012] Claim 4 The invention relates to an image forming apparatus having a configuration as claimed in claim 2, wherein the sheet feed control means discharges the sheet fed by the sheet feed means if the sheet detection means changes to a state where it does not detect a sheet before the specified time has elapsed after the sheet feed means has started the sheet feed operation.

[0013] Claim 5 The invention according to claim 4 In the image forming apparatus, the paper feed control means is configured to determine that the previous sheet is a large size error if the sheet detection means changes to a state where it does not detect a sheet before the specified time has elapsed after the sheet feed means has started the sheet feed operation.

[0015] Claim 6 The invention relates to an image forming apparatus having a configuration as claimed in claim 3, wherein the paper feed control means determines that the previous sheet is a large size error if the sheet detection means changes to a state where it does not detect a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs.

[0016] Claim 7 The invention according to claim 5 or 6 In the image forming apparatus, when the paper feed control means determines that the previous sheet has a large size error, it continues the transport operation of the previous sheet in the sheet transport path and discharges the previous sheet from the sheet transport path.

[0017] Claim 8 The invention relates to claims 1 to 7The image forming apparatus according to any one of claims 1 to 5, further comprising an image forming means for generating an image to be transferred onto a sheet transported along the sheet transport path, and transferring the image onto the sheet when the sheet passes a predetermined transfer position, wherein the image forming means starts an image generating operation at the same timing regardless of whether the paper feed timing is reset by the paper feed control means.

[0018] Claim 9 The invention relates to claims 1 to 8 In any one of the image forming apparatuses described above, the image forming apparatus further includes a position management means for managing position information of a sheet being transported along the sheet transport path, and the position management means is configured to determine that the leading edge of the sheet is at the detection position detected by the sheet detection means when the sheet feeding operation by the sheet feeding means is started at the re-set feeding timing, and to update the position information.

[0019] Claim 10 The present invention relates to a control method for an image forming apparatus including a sheet feeding means for feeding a sheet toward a sheet transport path, and a sheet detection means located downstream of the sheet feeding means for detecting the sheet, the control method including a control step of resetting the sheet feeding timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at a timing for feeding the sheet by the sheet feeding means, the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The control step includes: During a period from when the sheet feed timing is reset to when the sheet feed timing is reset, the sheet feed means is not caused to perform a sheet feed operation; This configuration is characterized in that it is determined whether or not to cause the paper feeding means to perform a sheet feeding operation at the reset paper feeding timing, depending on the detection result of the sheet detection means during the period from when the paper feeding timing is reset to when the reset paper feeding timing occurs. Claim 11The present invention relates to a control method for an image forming apparatus including a sheet feeding means for feeding a sheet toward a sheet transport path, and a sheet detection means located downstream of the sheet feeding means for detecting the sheet, the control method including a control step of resetting the sheet feeding timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at a timing for feeding the sheet by the sheet feeding means, the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The control step includes: During a period from when the sheet feed timing is reset to when the sheet feed timing is reset, the sheet feed means is not caused to perform a sheet feed operation; This configuration is characterized in that if the sheet detection means continues to detect a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs, the sheet feed operation by the paper feed means is started at the reset paper feed timing. Claim 12 The present invention relates to a control method for an image forming apparatus including a sheet feeding means for feeding a sheet toward a sheet transport path, and a sheet detection means located downstream of the sheet feeding means for detecting the sheet, the control method including a control step of resetting the sheet feeding timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at a timing for feeding the sheet by the sheet feeding means, the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The control step includes: During a period from when the sheet feed timing is reset to when the sheet feed timing is reset, the sheet feed means is not caused to perform a sheet feed operation; This configuration is characterized in that if the sheet detection means changes to a state in which it does not detect a sheet during the period from when the sheet feed timing is reset to when the reset sheet feed timing occurs, the sheet feed means is not caused to perform a sheet feed operation.

[0024] Claim 13 The invention according to claim 11 In the control method, the control step is characterized in that if the sheet detection means changes to a state where it does not detect a sheet before the specified time has elapsed after the sheet feeding operation by the sheet feeding means has started, the sheet fed by the sheet feeding means is discharged.

[0025] Claim 14 The invention according to claim 13In the control method, the control step is characterized in that if the sheet detection means changes to a state where it does not detect a sheet before the specified time has elapsed after the sheet feeding operation by the sheet feeding means has started, it is determined that the previous sheet is a large size error.

[0027] Claim 15 The invention according to claim 12 In the control method, the control step is characterized in that if the sheet detection means changes to a state where it does not detect a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs, it is determined that the previous sheet is a large size error.

[0028] Claim 16 The invention according to claim 14 or 15 In the control method, the control step is characterized in that, when it is determined that the previous sheet has a large size error, the control step continues the transport operation of the previous sheet in the sheet transport path and discharges the previous sheet from the sheet transport path.

[0029] Claim 17 The invention according to claim 10 ~ 16 In any one of the control methods, the image forming apparatus further includes an image forming means that generates an image to be transferred onto a sheet transported along the sheet transport path and transfers the image onto the sheet when the sheet passes a predetermined transfer position, and the control step is characterized in that it causes the image forming means to start an image generation operation at the same timing regardless of whether the paper feed timing is reset or not.

[0030] Claim 18 The invention according to claim 10 ~ 17In any one of the control methods, the present invention further includes a position management step for managing position information of the sheet being transported along the sheet transport path, and the position management step is characterized in that when the sheet feeding operation by the sheet feeding means is started at the re-set sheet feeding timing, it is determined that the leading edge of the sheet is at the detection position by the sheet detection means, and the position information is updated. Effect of the Invention

[0031] According to the present invention, even if the sheet detection unit has already detected a sheet when it is time to feed the next sheet, it is possible to continue the appropriate processing. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 illustrates an example of a configuration of an image forming apparatus. [Diagram 2] FIG. 2 is a diagram illustrating a control mechanism of the image forming apparatus. [Diagram 3] 4A and 4B are diagrams illustrating a sheet separating function of a paper feed roller. [Figure 4] FIG. 13 is a diagram showing a state in which a second sheet advances to the position of a paper feed roller when a first sheet is being fed. [Diagram 5] 5 is a timing chart showing a normal paper feeding operation. [Figure 6] FIG. 13 is a diagram showing a state in which a second sheet advances to the position of a sheet feed sensor when a first sheet is being fed. [Figure 7] 10 is a timing chart showing a paper feed operation in which the paper feed timing is reset. [Figure 8] 10 is a flowchart illustrating an example of a processing procedure performed by a job control unit. [Figure 9] 10 is a flowchart showing an example of a detailed process procedure of a first paper feed operation. [Figure 10] 10 is a flowchart showing an example of a detailed processing procedure of a second paper feed operation. [Figure 11]FIG. 13 is a diagram showing a state in which the size of the first sheet is larger than the set sheet size. [Figure 12] 10 is a flowchart illustrating an example of a detailed process procedure of a second paper feed operation in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, elements common to each other are designated by the same reference numerals, and redundant description thereof will be omitted.

[0034] (First embodiment) FIG. 1 is a diagram showing an example of the configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 shown in FIG. 1 is an apparatus that executes a print job by forming an image by electrophotography, and is an apparatus capable of forming a color image by a tandem method. Inside the apparatus main body 1a, the image forming apparatus 1 mainly has a paper feed conveying section 2 that feeds and conveys sheets 11 such as printing paper one by one, an image forming section 3 that forms an image on the sheet 11 conveyed by the paper feed conveying section 2, and a fixing section 4 that fixes the image formed on the sheet 11 by the image forming section 3. The image forming apparatus 1 also has a controller 9 inside the apparatus main body 1a that controls the operations of the paper feed conveying section 2, the image forming section 3, and the fixing section 4.

[0035] The paper feed conveying section 2 includes a paper feed tray 10 , a pickup roller 12 , a paper feed roller 13 , a conveying path 14 , a timing roller 15 , a secondary transfer roller 16 , and a paper discharge roller 17 .

[0036] The paper feed tray 10 is a container that stores a stack of sheets 11 such as printing paper. The paper feed tray 10 includes a lift plate 10a that can be raised and lowered with the sheets 11 stacked thereon, and a rear end regulating plate 10b that regulates the position of the rear end side of the sheets 11. The sheets 11 stored in the paper feed tray 10 are placed on the lift plate 10a, and are stored with the rear ends of the sheets abutting against the rear end regulating plate 10b. For example, the lift plate 10a rises with the sheets 11 stacked thereon, thereby pressing the topmost sheet 11 of the stack of sheets 11 against the pickup roller 12.

[0037] The pickup roller 12 contacts the uppermost sheet 11 among the multiple sheets 11 stored in the paper feed tray 10, and is driven to rotate in a predetermined direction (counterclockwise), thereby sending at least one sheet 11 downstream. The pickup roller 12 has an elastic member such as rubber wrapped around its surface, and rotates in a predetermined direction while being pressed downward. Therefore, the pickup roller 12 generates a frictional force between itself and the stack of sheets 11, and sends the sheets 11 downstream as it rotates in the predetermined direction. When the pickup roller 12 sends the first sheet 11 at the top downstream, it may also send the second and subsequent sheets 11 downstream together with the first sheet 11. This phenomenon in which the second and subsequent sheets 11 are sent downstream together with the first sheet 11 is called double feeding.

[0038] The paper feed roller 13 is provided downstream of the pickup roller 12, and supplies the sheet 11 sent out from the pickup roller 12 to a transport path 14 further downstream. In other words, the paper feed roller 13 is provided as a paper feed means that feeds the sheet 11 to the transport path 14. The paper feed roller 13 includes a drive roller 13a and a driven roller 13b, and has a sheet separation function that separates the topmost first sheet 11 from the second and subsequent sheets 11 by passing the sheet 11 sent out from the pickup roller 12 through a nip portion between the drive roller 13a and the driven roller 13b. The sheet separation function performed by the paper feed roller 13 will be described in detail later.

[0039] The sheet 11 is fed to the conveying path 14 by the paper feed roller 13 and conveyed along the conveying path 14 in the direction of the arrow F2. A timing roller 15 is provided at a predetermined position on the conveying path 14. The sheet 11 conveyed along the conveying path 14 stops once when its leading edge reaches the nip of the timing roller 15. The timing roller 15 is rotated at the timing when the image formed by the image forming unit 3 is conveyed to the position of the secondary transfer roller 16, and conveys the sheet 11 toward the secondary transfer roller 16. When the sheet 11 passes the position of the secondary transfer roller 16, the image formed by the image forming unit 3 is secondarily transferred onto the surface of the sheet 11. Incidentally, it is also possible to perform skew correction of the sheet 11 by temporarily stopping the conveyance of the sheet 11 with the leading edge of the sheet 11 abutting against the nip of the timing roller 15.

[0040] The sheet 11 onto which the image has been transferred at the position of the secondary transfer roller 16 then enters the fixing unit 4, where it is subjected to heat treatment and pressure treatment. As a result, the image transferred onto the sheet 11 is fixed onto the sheet 11. The fixing unit 4 includes a heating roller 28 and a pressure roller 29, and when the sheet 11 onto which the image has been transferred passes through a nip portion between the heating roller 28 and the pressure roller 29, it is subjected to heat treatment and pressure treatment, thereby fixing the image onto the sheet 11. Thus, when the sheet 11 passes through the fixing unit 4, a single printed matter on which the image has been printed is completed. Then, the sheet 11 onto which the image has been fixed is discharged by the paper discharge rollers 17 from the discharge port 5 onto the paper discharge tray 6 provided at the top of the device main body 1a.

[0041] The above-described paper feed conveying section 2 includes a paper feed sensor 18 downstream of the paper feed roller 13. The paper feed sensor 18 is provided at a position downstream of the paper feed roller 13 and spaced a predetermined distance from the paper feed roller 13, and is a sheet detection means that detects the sheet 11 fed from the paper feed roller 13 to the conveying path 14. For example, the paper feed sensor 18 is configured with a light reflection type sensor or a light transmission type sensor. The paper feed sensor 18 is a sensor in which the sensor output is turned off when the sheet 11 is not present at a predetermined detection position downstream of the paper feed roller 13, and the sensor output is turned on when the paper feed sensor 18 detects that the sheet 11 is present at the predetermined detection position.

[0042] Furthermore, the paper feed conveying section 2 is provided with a timing sensor 19 upstream of the timing roller 15. The timing sensor 19 is provided at a predetermined position upstream of the timing roller 15, and detects the sheet 11 entering the nip portion of the timing roller 15. This timing sensor 19 is also composed of, for example, a light reflection type sensor or a light transmission type sensor. The timing sensor 19 is a sensor in which the sensor output is turned off when the sheet 11 is not detected, and the sensor output is turned on when the sheet 11 is detected.

[0043] The image forming unit 3 forms toner images of four colors, Y (yellow), M (magenta), C (cyan), and K (black), and primarily transfers the toner images of each color in a superimposed state onto the intermediate transfer belt 23, which is driven in a circulating manner. This forms a color image on the intermediate transfer belt 23. Then, the image forming unit 3 secondarily transfers the color image onto the surface of the sheet 11 transported by the paper feed transport unit 2 when the color image formed on the intermediate transfer belt 23 passes a position facing the secondary transfer roller 16.

[0044] This image forming section 3 includes a plurality of exposure units 21 (21Y, 21M, 21C, 21K) corresponding to each of the colors Y, M, C, and K, a plurality of image forming units 20 (20Y, 20M, 20C, 20K) corresponding to each of the colors, primary transfer rollers 22 (22Y, 22M, 22C, 22K) arranged opposite each image forming unit 20, a plurality of toner bottles 26 (26Y, 26M, 26C, 26K) corresponding to each of the colors, an intermediate transfer belt 23 formed by an endless belt, a drive roller 25 that drives the intermediate transfer belt 23 in a circulating manner, and a driven roller 24 that is driven to rotate by the circulating movement of the intermediate transfer belt 23.

[0045] The exposure units 21 (21Y, 21M, 21C, 21K) are disposed in the vicinity of the image forming units 20 (20Y, 20M, 20C, 20K) corresponding to each color. In this embodiment, the exposure units 21 are provided below each image forming unit 20. The exposure units 21 irradiate the surface of the image carrier (photosensitive drum) of the image forming unit 20 corresponding to each color with scanning light based on image data, thereby exposing the surface of the image carrier to form an electrostatic latent image.

[0046] Image forming units 20 (20Y, 20M, 20C, 20K) corresponding to each color are provided below the intermediate transfer belt 23. Toner bottles 26 (26Y, 26M, 26C, 26K) are disposed above the intermediate transfer belt 23 and supply developer containing toner of each color to each image forming unit 20 (20Y, 20M, 20C, 20K).

[0047] Each image forming unit 20 is disposed at a position facing the primary transfer roller 22 with the intermediate transfer belt 23 interposed therebetween. The image forming unit 20 includes an image carrier disposed to face the primary transfer roller 22. The image carrier is, for example, a photosensitive drum extending from the front side to the back side of the image forming apparatus, and has a photosensitive layer on its surface. When an image is formed in the image forming unit, the image carrier is rotated in a predetermined direction (clockwise direction). The image forming unit includes a cleaner, a charging unit, and a developing device around the image carrier. The charging unit charges the surface of the image carrier to a predetermined charge. When the surface of the image carrier is charged to a predetermined charge by the charging unit, an electrostatic latent image is formed on the surface of the image carrier by the scanning light emitted from the exposure unit. The developing device applies a developer consisting of toner and carrier to the surface of the image carrier, thereby visualizing the electrostatic latent image with toner and forming a toner image on the image carrier. The toner image thus formed on the surface of the image carrier is primarily transferred onto the intermediate transfer belt 23 by a bias voltage applied from the primary transfer roller 22 when the toner image comes into contact with the intermediate transfer belt 23 which moves in a circular motion in the direction of the arrow F1.

[0048] Each image forming unit 20 primarily transfers a toner image of each color onto the intermediate transfer belt 23 in a superimposed manner, thereby forming a color image on the surface of the intermediate transfer belt 23. This color image circulates in the direction of arrow F1 together with the intermediate transfer belt 23. Then, when the intermediate transfer belt 23 passes between the secondary transfer roller 16 and the drive roller 25, it is joined to the surface of the sheet 11 sent out from the timing roller 15, and is secondarily transferred onto the surface of the sheet 11 by the bias voltage applied from the secondary transfer roller 16.

[0049] Next, Fig. 2 is a diagram showing a control mechanism of the image forming apparatus 1. In addition to the above-mentioned configuration, the image forming apparatus 1 is equipped with an operation panel 8 that can be operated by the user, and a communication interface 49. The operation panel 8 is equipped with a display unit 8a that displays various operation screens that can be operated by the user, and an operation unit 8b that accepts operations by the user. The communication interface 49 is for connecting the image forming apparatus 1 to a network such as a LAN (Local Area Network) and communicating with an external device connected to the network. For example, the image forming apparatus 1 can receive a print job from an external device via this communication interface 49.

[0050] The controller 9 includes a CPU 40 and a storage unit 41. The CPU 40 is a hardware processor that reads and executes a program 42 stored in the storage unit 41. The storage unit 41 is a non-volatile storage device configured, for example, by a hard disk drive (HDD) or a solid state drive (SSD). The storage unit 41 stores the program 42 executed by the CPU 40, a sheet size 43 of the sheets 11 accommodated in the paper feed tray 10, and position information 44 indicating the current position of the sheet 11 being conveyed by the paper feed conveying unit 2 in the conveying path 14.

[0051] The CPU 40 executes the program 42 to function as a sheet size setting unit 50 and a job control unit 51 .

[0052] The sheet size setting unit 50 functions when a stack of sheets 11 is set in the paper feed tray 10 by the user. For example, when the sheet size setting unit 50 detects that a stack of sheets 11 is set in the paper feed tray 10, it displays an operation screen for performing setting operations related to sheets on the display unit 8a of the operation panel 8. The user operates the operation screen to input sheet information including the sheet size. The sheet size setting unit 50 detects the sheet size set in the paper feed tray 10 based on user operation information obtained from the operation unit 8b of the operation panel 8, and stores information about the sheet size as the sheet size 43 in the storage unit 41. In addition, the sheet size setting unit 50 is not necessarily limited to a unit that detects the sheet size based on a setting operation by the user, and may automatically detect the sheet size of the sheets 11 set in the paper feed tray 10 and store the automatically detected sheet size 43 in the storage unit 41.

[0053] The job control unit 51 functions when a print job is received via, for example, the communication interface 49, and controls the execution of the print job in the image forming apparatus 1. The job control unit 51 controls the operations of the paper feed conveyance unit 2, the image forming unit 3, and the fixing unit 4, thereby generally controlling the operations of conveying the sheet 11 along the conveyance path 14, transferring the toner image to the sheet 11, and discharging the sheet 11 on which the image is printed onto the paper output tray 6 after the toner image is fixed to the sheet 11 in the fixing unit 4. The job control unit 51 includes a paper feed control unit 52, a position management unit 53, and an image control unit 54.

[0054] When a print job starts, the paper feed control unit 52 controls the paper feed transport unit 2 to feed sheets 11 one by one from the paper feed tray 10 to the transport path 14 and transport the sheets 11 along the transport path 14. For example, if the print job is a job for continuously printing images on multiple sheets 11, the paper feed control unit 52 continuously feeds the multiple sheets 11 one by one from the paper feed tray 10. At this time, the paper feed control unit 52 transports the multiple sheets 11 sequentially along the transport path 14 while maintaining a constant sheet interval between the multiple sheets 11.

[0055] For example, the paper feed conveying unit 2 includes a drive motor 30 for driving the above-mentioned pickup roller 12, paper feed roller 13, timing roller 15, and paper discharge roller 17, and a clutch mechanism 31 provided in a power transmission path from the drive motor 30 to each of the pickup roller 12, paper feed roller 13, timing roller 15, and paper discharge roller 17. The clutch mechanism 31 is capable of switching between a state in which the drive force of the drive motor 30 is transmitted to each roller and a state in which it is not transmitted.

[0056] When performing a paper feed operation to feed sheets 11 from paper feed tray 10 to transport path 14, paper feed control unit 52 operates drive motor 30 and controls clutch mechanism 31 so that power from drive motor 30 is transmitted to pickup roller 12 and paper feed roller 13. When stopping the paper feed operation, paper feed control unit 52 operates drive motor 30 while controlling clutch mechanism 31 so that power from drive motor 30 is not transmitted to pickup roller 12 and paper feed roller 13, thereby stopping pickup roller 12 and paper feed roller 13. Similarly to the above, paper feed control unit 52 also controls clutch mechanism 31 for timing roller 15, thereby allowing timing roller 15 to rotate or stop.

[0057] In addition, when the sheet feeding control unit 52 starts the sheet feeding operation for feeding the sheet 11, the sheet feeding control unit 52 controls the conveying operation of the sheet 11 according to the detection states of the sheet 11 by the sheet feeding sensor 18 and the timing sensor 19, respectively.

[0058] The position management unit 53 manages the current position of the sheet 11 fed from the sheet feed tray 10 as the sheet feed control unit 52 starts the feeding operation of the sheet 11. For example, when the leading edge of the sheet 11 is detected by the sheet feed sensor 18 after the feeding operation of the sheet feed control unit 52 starts, the position management unit 53 can determine that the leading edge of the sheet 11 is at the position detected by the sheet feed sensor 18. In addition, the conveying speed of the sheet 11 conveyed along the conveying path 14 by the sheet feed control unit 52 is known. Therefore, the position management unit 53 sequentially updates the leading edge position of the sheet 11 according to the elapsed time after the leading edge of the sheet 11 is detected by the sheet feed sensor 18. Then, when the leading edge of the sheet 11 is detected by the timing sensor 19, the position management unit 53 can determine that the leading edge of the sheet 11 is at the position detected by the timing sensor 19. In this way, the position management unit 53 determines the current position of the sheet 11 conveyed along the conveying path 14, and sequentially updates the position information 44 stored in the storage unit 41.

[0059] When feeding a plurality of sheets 11 continuously, the feed control unit 52 reads out the sheet size 43 stored in the storage unit 41 and sets an appropriate sheet interval based on the sheet size 43. The sheet interval in this case is, for example, the interval from the leading edge of the previously fed sheet 11 to the leading edge of the next fed sheet 11. The feed control unit 52 feeds a plurality of sheets 11 continuously so as to maintain the sheet interval that is preset based on the sheet size 43. More specifically, when feeding the first sheet 11, the feed control unit 52 reads out the position information 44 that is successively updated by the position management unit 53 and constantly grasps the leading edge position of the first sheet 11. Then, when the leading edge of the first sheet 11 reaches a predetermined position according to the preset sheet interval, the feed control unit 52 determines that it is time to feed the next sheet 11 and starts a feed operation to feed the next sheet 11 from the feed tray 10. In this manner, the sheet feed control unit 52 controls the sheet interval between two sheets 11 successively fed from the sheet feed tray 10 to be a predetermined interval.

[0060] Furthermore, when the paper feed control unit 52 starts the paper feed operation at the timing for feeding the sheet 11, it can predict that the sheet 11 will reach the detection position of the timing sensor 19 within a predetermined time. In other words, if the timing sensor 19 does not detect the sheet 11 even after a predetermined time has elapsed since the start of the paper feed operation of the sheet 11, it is determined that the fed sheet 11 has become clogged and caused a paper feed jam. Therefore, if the timing sensor 19 does not detect the sheet 11 within a predetermined time from the start of the paper feed operation of the sheet 11, the paper feed control unit 52 detects that a paper feed jam has occurred in the paper feed operation and stops the execution of the print job in the image forming apparatus 1.

[0061] Furthermore, the paper feed control unit 52 can measure the time required from when the leading edge of the sheet 11 passes the timing sensor 19 until when the trailing edge of the sheet 11 passes the timing sensor 19, and detect the sheet size of the sheet 11 currently being transported based on the measured time.

[0062] The image control unit 54 controls the image forming unit 3 and the fixing unit 4 in conjunction with the conveying operation of the sheet 11 by the paper feed conveying unit 2 to form a toner image to be transferred to the sheet 11 on the intermediate transfer belt 23, and secondarily transfers the toner image formed on the intermediate transfer belt 23 onto the sheet 11 passing the position of the secondary transfer roller 16. For example, when the leading edge of the sheet 11 conveyed by the paper feed conveying unit 2 reaches a predetermined position, the image control unit 54 starts an image forming operation by the image forming unit 3 to form an image to be transferred onto the sheet 11. As a result, a toner image of each color is formed in the image forming unit 20 corresponding to each color, and the toner image of each color is primarily transferred to the intermediate transfer belt 23 in sequence. Then, the image control unit 54 secondarily transfers the toner image primarily transferred onto the intermediate transfer belt 23 onto the surface of the sheet 11 when the sheet 11 conveyed by the paper feed conveying unit 2 passes the position of the secondary transfer roller 16.

[0063] The image control unit 54 also controls the operation of the fixing unit 4. That is, the image control unit 54 drives a heater (not shown) provided on the heating roller 28 to raise the temperature of the heating roller 28 to a predetermined temperature, and rotates the heating roller 28 and the pressure roller 29 while pressing the pressure roller 29 against the heating roller 28 with a predetermined pressure. As a result, the sheet 11 is subjected to a heat treatment and a pressure treatment when passing through the nip portion between the heating roller 28 and the pressure roller 29, and the image transferred to the sheet 11 can be fixed to the sheet 11.

[0064] Next, FIG. 3 is a diagram for explaining the sheet separation function of the paper feed roller 13. As described above, the paper feed roller 13 includes the drive roller 13a and the driven roller 13b. When the paper feed operation of the sheet 11 is started, the drive roller 13a is driven to rotate in a predetermined direction (counterclockwise direction). The driven roller 13b is disposed below the drive roller 13a so as to contact the roller surface of the drive roller 13a. Therefore, the driven roller 13b is rotated in the opposite direction to the drive roller 13a as the drive roller 13a rotates. However, the driven roller 13b is provided with a torque limiter, and the driven roller 13b does not rotate unless the torque acting on the driven roller 13b exceeds a predetermined value.

[0065] For example, as shown in FIG. 3A, when one sheet 11a is sent toward the feed roller 13 by the pickup roller 12, the leading edge of the sheet 11a advances to the nip between the drive roller 13a and the driven roller 13b. The sheet 11a sandwiched between the drive roller 13a and the driven roller 13b is transported downstream by the rotation of the drive roller 13a. At this time, the driven roller 13b is in contact with the lower surface side of the sheet 11a. As the sheet 11a moves downstream, the torque acting on the driven roller 13b due to the frictional force with the sheet 11a exceeds a predetermined value, so that the driven roller 13b is rotated.

[0066] Also, as shown in FIG. 3(b), when multiple sheets 11 are fed from the pickup roller 12 to the paper feed roller 13, at least the first sheet 11a at the top of the multiple sheets 11 is sandwiched in the nip between the drive roller 13a and the driven roller 13b, and the first sheet 11a is transported downstream by the rotation of the drive roller 13a. When the first sheet 11a is transported downstream, when the second sheet 11b advances to the nip between the drive roller 13a and the driven roller 13b, the driven roller 13b comes into contact with the lower surface side of the second sheet 11b. At this time, since no torque exceeding a predetermined value acts on the driven roller 13b, the driven roller 13b is stopped without rotating, and the second and subsequent sheets 11b are stopped without advancing downstream. As a result, the paper feed roller 13 can transport only the first sheet 11a downstream.

[0067] Also, as shown in FIG. 3C, when a plurality of sheets 11 are fed from the pickup roller 12 to the feed roller 13 in a multi-feed manner, for example, the second and third sheets 11b and 11c may move downstream as the first sheet 11a is conveyed downstream. In this case, when the third sheet 11b advances to the nip between the drive roller 13a and the driven roller 13b, the third sheet 11b stops advancing downstream due to contact with the driven roller 13b. However, the second sheet 11b does not come into contact with the driven roller 13b, and thus the second sheet 11b is fed further downstream together with the first sheet 11a in a multi-feed manner. When such a phenomenon occurs in continuous feeding, the leading edge of the next sheet 11b may advance to the detection position by the feed sensor 18 when the previous sheet 11a is fed.

[0068] Next, a normal sheet feeding operation during continuous sheet feeding controlled by the sheet feeding control unit 52 will be described. When continuously feeding a plurality of sheets 11, the sheet feeding control unit 52 determines the timing of feeding the second and subsequent sheets 11 on the assumption that the second and subsequent sheets 11 are in a predetermined reference position. The predetermined reference position is, for example, a position where the rear end of the second and subsequent sheets 11 contacts the rear end regulating plate 10b of the sheet feeding tray 10. After feeding the first sheet 11a, when the leading end of the first sheet 11a reaches a predetermined position, the sheet feeding control unit 52 determines that the sheet interval between the first sheet 11a and the second sheet 11b in the predetermined reference position has become a predetermined interval, and detects that it is time to feed the second sheet 11b.

[0069] However, as described above, when the first sheet 11a is fed, the second sheet 11b may be double-fed and move downstream. FIG. 4 is a diagram showing a state in which the second sheet 11b advances to the position of the feed roller 13 when the first sheet 11a is fed. In this case, as shown in FIG. 4(a), when it is detected that it is time to feed the second sheet 11b, the second sheet 11b has already advanced to the position of the feed roller 13 downstream of the reference position. If the second sheet 11b is fed to the conveying path 14 in this state, the interval between the first sheet 11a and the second sheet 11b may become smaller than the preset sheet interval, and a jam may occur. Therefore, the feed control unit 52 starts the feed operation of the second sheet 11b at the feed timing of the second sheet 11b, and then adjusts the sheet interval based on the timing at which the leading edge of the second sheet 11b is detected by the feed sensor 18. That is, as shown in FIG. 4B, the feed control unit 52 temporarily stops the feed operation of the second sheet 11b when the leading edge of the second sheet 11b reaches the detection position of the feed sensor 18 and the feed sensor 18 switches from off to on. At this time, the position information 44 of the second sheet 11b is updated. Meanwhile, the feed control unit 52 continues the conveying operation of the first sheet 11a. Then, the feed control unit 52 resumes the feed operation of the second sheet 11b when the interval between the first sheet 11a and the second sheet 11b becomes a predetermined sheet interval. This allows the interval between the first sheet 11a and the second sheet 11b to be adjusted to a predetermined sheet interval.

[0070] FIG. 5 is a timing chart showing the normal sheet feeding operation as described above. As shown in FIG. 5, after feeding the first sheet 11a, when the sheet feeding control unit 52 detects that it is the sheet feeding timing T0 of the second sheet 11b, it starts the sheet feeding operation for feeding the second sheet 11b. At this time, the sheet feeding sensor 18 is in the OFF state because it does not detect the sheet 11. In addition, the sheet feeding control unit 52 starts measuring time when the sheet feeding operation of the second sheet 11b starts at the sheet feeding timing T0. After that, when the leading edge of the second sheet 11b is detected by the sheet feeding sensor 18, the sheet feeding sensor 18 switches from the OFF state to the ON state. When the second sheet 11b is fed from a position downstream of the predetermined reference position, the timing T1 at which the leading edge of the second sheet 11b is detected by the sheet feeding sensor 18 is earlier than when the second sheet 11b is fed from the predetermined reference position. Therefore, the paper feed control unit 52 temporarily stops the paper feed operation of the second sheet 11b at timing T1 when the paper feed sensor 18 detects the second sheet 11b. Then, the paper feed control unit 52 judges whether or not the time when the measurement was started at the paper feed timing T0 has measured the predetermined time TP. That is, since the time (predetermined time TP) required for the leading edge of the second sheet 11b to reach the detection position of the paper feed sensor 18 when the second sheet 11b is fed from a predetermined reference position is known, the paper feed control unit 52 judges whether or not the elapsed time from the paper feed timing T0 has reached the predetermined time TP, thereby detecting the timing T2 when the sheet 11b will reach the position of the paper feed sensor 18 when the sheet 11b is fed from the predetermined reference position.

[0071] When it is detected that timing T2 has arrived, the sheet feed control unit 52 resumes the sheet feed operation of the second sheet 11b. As a result, the interval between the first sheet 11a and the second sheet 11b becomes the sheet interval set in advance. Therefore, the second sheet 11b that is fed again after timing T2 is conveyed while maintaining an appropriate sheet interval between it and the preceding first sheet 11a.

[0072] Then, the image forming operation by the image forming unit 3 is started at timing T3 when the leading edge of the second sheet 11b passes a predetermined position on the conveying path 14. Also, when the trailing edge of the second sheet 11b passes the detection position of the paper feed sensor 18, the paper feed sensor 18 switches from the ON state to the OFF state.

[0073] Furthermore, when the leading edge of second sheet 11b reaches the position of timing sensor 19, paper feed control unit 52 temporarily stops the transport operation of second sheet 11b. Thereafter, paper feed control unit 52 resumes the transport operation of second sheet 11b at predetermined timing T6, which is the timing when the toner image secondarily transferred to intermediate transfer belt 23 in image forming unit 3 is transported to the position of secondary transfer roller 16, and supplies sheet 11b toward secondary transfer roller 16. As a result, the toner image is secondarily transferred onto second sheet 11b.

[0074] Furthermore, when the feeding timing T0 for the second sheet 11b is reached and the feeding operation of the second sheet 11b is started, the feeding control unit 52 sets a jam detection time for detecting a feeding jam to a predetermined time Ta. This predetermined time Ta is set as the time required for the second sheet 11b to reach the position of the timing sensor 19 when fed from a predetermined reference position, or as a time slightly longer than that time. Then, after the feeding operation of the second sheet 11b is started, if the timing sensor 19 does not detect the sheet 11b even after the predetermined time Ta has elapsed, the feeding control unit 52 detects a feeding jam. In this case, the feeding control unit 52 immediately stops the conveying operation of the sheet 11b to prevent damage to the sheet 11b. The above is the normal feeding operation during continuous feeding.

[0075] Next, a paper feed operation in the case where the normal paper feed operation described above cannot adjust the sheet interval to an appropriate value when feeding the second and subsequent sheets will be described. FIG. 6 is a diagram showing a state in which the normal paper feed operation described above cannot be performed, and the second sheet 11b advances to the position of the paper feed sensor 18 when the first sheet 11a is fed. As shown in FIG. 6, when the second sheet 11b is fed in a double feed while the first sheet 11a is being fed, if the leading edge of the second sheet 11b reaches the position of the paper feed sensor 18, the paper feed sensor 18 is already in an ON state when it is detected that it is the timing to feed the second sheet 11b. In this case, even if the paper feed operation of the second sheet 11b is started, the timing when the paper feed sensor 18 switches from OFF to ON cannot be detected, and therefore the paper feed operation of the second sheet 11b cannot be temporarily stopped. Therefore, the sheet interval cannot be adjusted in the normal paper feed operation described above.

[0076] Therefore, if the paper feed sensor 18 is already on at the time when the second sheet 11b is to be fed, the paper feed control unit 52 resets the feed timing for the second sheet 11b to a timing delayed by a predetermined time.

[0077] FIG. 7 is a timing chart showing a sheet feeding operation in which the sheet feeding timing is reset. As shown in FIG. 7, when the sheet feeding sensor 18 is in an ON state at the sheet feeding timing T0 of the second sheet 11b after the first sheet 11a is fed, the sheet feeding control unit 52 does not start the sheet feeding operation of the second sheet 11b, and resets the sheet feeding timing T0 to a timing T2 delayed by a predetermined time TP. In this case, the predetermined time TP is the time required for the leading edge of the second sheet 11b to reach the detection position of the sheet feeding sensor 18 when the second sheet 11b is fed from a predetermined reference position, as in FIG. 5. Then, the sheet feeding control unit 52 starts measuring time from the timing T0, and detects that the reset sheet feeding timing T2 has been reached after measuring the predetermined time TP. When the reset sheet feeding timing T2 has been detected, the sheet feeding control unit 52 starts the sheet feeding operation of the second sheet 11b. As a result, the second sheet 11b is fed toward the downstream side of the conveying path 14.

[0078] That is, at timing T0, the leading edge of the second sheet 11b has reached the position of the sheet feed sensor 18, so that the interval between the preceding first sheet 11a and the following second sheet 11b is narrower than the preset sheet interval. Therefore, the sheet feed control unit 52 does not perform the sheet feed operation of the second sheet 11b at timing T0, but resets the sheet feed timing of the second sheet 11b to timing T2, which is delayed by a predetermined time TP from the original timing T0, thereby widening the sheet interval between the preceding first sheet 11a and the second sheet 11b, and starts the sheet feed operation of the second sheet 11b at timing T2 when the sheet interval becomes appropriate. This makes it possible to convey the second sheet 11b in a state where the interval between the first sheet 11a and the second sheet 11b is close to the preset sheet interval, and it is possible to prevent the second sheet 11b from catching up with the first sheet 11a from causing a jam.

[0079] Furthermore, when the feeding operation of second sheet 11b starts at reset feeding timing T2, position management unit 53 determines that the leading edge of second sheet 11b is at the position of feeding sensor 18, and updates position information 44 of second sheet 11b. Then, position management unit 53 successively updates position information 44 of second sheet 11b as the feeding operation of second sheet 11b progresses.

[0080] Then, the image forming operation by the image forming unit 3 is started at timing T3 when the leading edge of the second sheet 11b passes a predetermined position on the conveying path 14. Also, when the trailing edge of the second sheet 11b passes the detection position of the paper feed sensor 18, the paper feed sensor 18 switches from the ON state to the OFF state.

[0081] When the leading edge of second sheet 11b fed at timing T2 reaches the position of timing sensor 19 at timing T4, feed control unit 52 temporarily stops the transport operation of second sheet 11b. Thereafter, feed control unit 52 resumes the transport operation of second sheet 11b at predetermined timing T6, which is the timing when the toner image secondarily transferred to intermediate transfer belt 23 in image forming unit 3 is transported to the position of secondary transfer roller 16, and supplies sheet 11b toward secondary transfer roller 16. As a result, the toner image is secondarily transferred onto second sheet 11b.

[0082] Furthermore, when starting the feeding operation of the second sheet 11b at the reset feeding timing T2, the feeding control unit 52 sets the jam detection time for detecting a feeding jam to a predetermined time Tb and starts measuring time. This predetermined time Tb is set as the time required for the second sheet 11b to reach the position of the timing sensor 19 when the leading edge of the second sheet 11b is at the position of the feeding sensor 18, or a time slightly longer than that time. Therefore, the predetermined time Tb is shorter than the predetermined time Ta when a normal feeding operation is performed. After starting the feeding operation of the second sheet 11b, when the timing sensor 19 does not detect the sheet 11b even after the predetermined time Tb has elapsed, the feeding control unit 52 detects a feeding jam. In this case, the feeding control unit 52 immediately stops the conveying operation of the sheet 11b to prevent damage to the sheet 11b. The above is the feeding operation that resets the feeding timing and starts at the reset feeding timing.

[0083] In the above, the relationship between the first sheet 11a and the second sheet 11b has been mainly exemplified, but when the second or subsequent sheet 11 is fed, the relationship between the preceding sheet 11a and the succeeding sheet 11b is also the same as described above.

[0084] Next, a process performed by the job control unit 51 will be described. FIGS. 8 to 10 are flowcharts showing an example of the process performed by the job control unit 51. Prior to the start of the process shown in FIG. 8, the job control unit 51 sets the sheet interval when performing continuous paper feeding based on the sheet size 43 stored in the storage unit 41. As shown in FIG. 8, when the job control unit 51 starts the execution of a print job, it puts the paper feed control unit 52 into operation. Then, the paper feed control unit 52 starts the paper feed operation of the first sheet 11a (step S1). When the paper feed control unit 52 starts the paper feed operation of the first sheet 11a, it determines whether the first sheet 11a has been detected by the paper feed sensor 18 (step S2). Then, it waits until the first sheet 11a is detected by the paper feed sensor 18. When the first sheet 11a is detected by the paper feed sensor 18 (YES in step S2), the position management unit 53 starts to operate. Then, the position management unit 53 generates position information indicating that the leading edge of the first sheet 11a is at the position of the paper feed sensor 18, and updates the position information 44 in the storage unit 41 (step S3). Furthermore, the position management unit 53 thereafter sequentially updates the position information 44 of the first sheet 11a as the conveying operation of the first sheet 11a continues (step S3). Therefore, as the first sheet 11a advances along the conveying path 14, the position information 44 of the first sheet 11a stored in the storage unit 41 is sequentially updated.

[0085] The feed control unit 52 monitors the position information 44 of the first sheet 11a, and judges whether the leading edge of the first sheet 11a reaches a predetermined position, and thus it is the feed timing T0 of the next sheet 11b, which is the second sheet (step S4). As a result, when it is judged that it is the feed timing T0 of the next sheet 11b (YES in step S4), the feed control unit 52 judges whether the feed sensor 18 is in a non-detecting state of the sheet 11 (step S5). That is, the feed control unit 52 judges whether the feed sensor 18 is in an OFF state. When the feed sensor 18 is in an OFF state (YES in step S5), the feed control unit 52 performs a first feed operation (step S6). The first feed operation is the normal feed operation described above. When the feed sensor 18 is in an ON state (NO in step S5), the feed control unit 52 performs a second feed operation (step S7). The second sheet feeding operation is an operation in which the sheet feeding timing is reset, and the next sheet 11b is fed at the reset sheet feeding timing.

[0086] FIG. 9 is a flowchart showing an example of a detailed processing procedure of the first sheet feeding operation (step S6). When the sheet feeding control unit 52 starts the first sheet feeding operation, it sets the jam detection time to a predetermined time Ta (step S10). Then, the sheet feeding control unit 52 starts the sheet feeding operation of the next sheet 11b (step S11) and starts measuring time (step S12). After starting the feeding of the next sheet 11b, the sheet feeding control unit 52 judges whether the sheet feeding sensor 18 has detected the sheet 11b (step S13), and when the sheet 11b is detected by the sheet feeding sensor 18 (YES in step S13), it temporarily stops the sheet feeding operation of the sheet 11b (step S14). Then, when the time that was started to be measured in step S12 reaches the predetermined time TP, the sheet feeding control unit 52 judges that it is the timing T2 to feed again (YES in step S15) and resumes the sheet feeding operation of the next sheet 11b (step S16). As a result, the next sheet 11b is conveyed while maintaining an appropriate sheet interval between it and the preceding sheet 11a.

[0087] Thereafter, the paper feed control unit 52 determines whether or not the next sheet 11b has been detected by the timing sensor 19 (step S17). If the next sheet 11b has not been detected by the timing sensor 19 (NO in step S17), the paper feed control unit 52 determines whether or not the time measurement started in step S12 has measured a predetermined time Ta (step S21).

[0088] If the timing sensor 19 detects the next sheet 11b before the predetermined time Ta has elapsed (YES in step S17), the feed control unit 52 temporarily stops the feed operation of the next sheet 11b with the leading edge of the next sheet 11b abutting against the nip of the timing roller 15 (step S19). After that, the feed control unit 52 waits until timing T6 (see FIG. 5) at which the toner image formed on the intermediate transfer belt 23 in the image forming unit 3 can be secondarily transferred to the sheet 11b (step S19), and when it detects that timing T6 has been reached (YES in step S19), it rotates the timing roller 15 to resume the feed operation of the sheet 11b (step S20). This allows the toner image to be appropriately secondarily transferred to the sheet 11b.

[0089] On the other hand, if the predetermined time Ta has elapsed without the timing sensor 19 detecting the sheet 11b (YES in step S21), the sheet feed control unit 52 determines that a sheet feed jam has occurred during feeding of the sheet 11b (step S22). In this case, the sheet feed control unit 52 stops the sheet feed operation of the sheet 11b (step S23). Then, the sheet feed control unit 52 temporarily suspends the execution of the print job by the job control unit 51.

[0090] Next, FIG. 10 is a flowchart showing an example of a detailed processing procedure of the second sheet feeding operation (step S7). When the second sheet feeding operation is started, the sheet feeding control unit 52 resets the sheet feeding timing T2 (see FIG. 7) delayed by a predetermined time TP from the current timing T0 without starting the sheet feeding operation of the next sheet 11b (step S30). Then, the sheet feeding control unit 52 starts measuring time (step S31) and judges whether the reset sheet feeding timing T2 has arrived (step S32). If the reset sheet feeding timing T2 has arrived (YES in step S32), the sheet feeding control unit 52 shortens the jam detection time to a predetermined time Tb shorter than that in the first sheet feeding operation (step S33). Then, the sheet feeding control unit 52 starts the sheet feeding operation of the next sheet 11b (step S34) and starts measuring time again (step S35).

[0091] Thereafter, the paper feed control unit 52 determines whether or not the next sheet 11b has been detected by the timing sensor 19 (step S36). If the next sheet 11b has not been detected by the timing sensor 19 (NO in step S36), the paper feed control unit 52 determines whether or not the time measurement started in step S35 has measured a predetermined time Tb (step S40).

[0092] If the timing sensor 19 detects the next sheet 11b before the predetermined time Tb has elapsed (YES in step S36), the feed control unit 52 temporarily stops the feed operation of the next sheet 11b with the leading edge of the next sheet 11b abutting against the nip of the timing roller 15 (step S37). Then, the feed control unit 52 waits until timing T6 (see FIG. 7) at which the toner image formed on the intermediate transfer belt 23 in the image forming unit 3 can be secondarily transferred to the sheet 11b (step S38), and when it detects that timing T6 has been reached (YES in step S38), it rotates the timing roller 15 to resume the feed operation of the sheet 11b (step S39). This allows the toner image to be appropriately secondarily transferred to the sheet 11b.

[0093] On the other hand, if the predetermined time Tb has elapsed without the timing sensor 19 detecting the sheet 11b (YES in step S40), the sheet feed control unit 52 determines that a sheet feed jam has occurred during sheet feed of the sheet 11b (step S41). In this case, the sheet feed control unit 52 stops the sheet feed operation of the sheet 11b (step S42). Then, the sheet feed control unit 52 temporarily suspends the execution of the print job by the job control unit 51. In this second sheet feed operation, the predetermined time Tb is set shorter than that in the first sheet feed operation, so that if a sheet feed jam occurs after the start of the sheet feed operation of the sheet 11b, the occurrence of the sheet feed jam can be detected early and the sheet feed operation can be stopped. Therefore, it is possible to prevent the sheet 11b from being severely damaged due to the sheet feed operation continuing for a long time.

[0094] Returning to the flowchart of Fig. 8, when the feeding operation of the next sheet 11b is completed in step S6 or S7, the feeding control unit 52 judges whether the print job is completed or not (step S8). As a result, if the print job is not completed and the next sheet needs to be fed (NO in step S8), the processing by the feeding control unit 52 returns to step S3 and the above-mentioned processing is repeated. On the other hand, if the print job is completed (YES in step S8), the processing by the job control unit 51 is completed.

[0095] As described above, the image forming apparatus 1 of the present embodiment is configured to reset the feed timing T0 for feeding the next sheet 11b to a timing T2 delayed by a predetermined time TP when the feed sensor 18 has already detected the sheet 11 when the previously fed sheet 11a reaches a predetermined position and the sheet feed timing T0 for feeding the next sheet 11b is reached. With this configuration, it is not necessary to temporarily stop the feed operation after starting the feed operation of the next sheet 11b, and it is possible to prevent the sheet interval between the previous sheet 11a and the next sheet 11b from becoming extremely narrow. As a result, even if the feed sensor 18 detects the sheet 11 at the feed timing T0, it is not detected as an error, and it is possible to continue the execution of the job.

[0096] Furthermore, in this embodiment, regardless of whether the first feeding operation (step S6) or the second feeding operation (step S7) is performed, the timing T3 at which the image forming operation by the image forming unit 3 starts is the same, based on the feeding timing T0 of the next sheet 11b. Therefore, regardless of whether the first feeding operation or the second feeding operation is performed when feeding the next sheet 11b, the throughput of the image forming apparatus 1 does not decrease, and it is possible to maintain a constant throughput.

[0097] Second embodiment Next, a second embodiment of the present invention will be described. In the first embodiment, a feeding mode was described in which the second sheet 11b is double-fed when the first sheet 11a is fed, and the feeding sensor 18 is already in the ON state when the feeding timing T0 of the second sheet 11b arrives. However, there are other reasons why the feeding sensor 18 is already in the ON state at the feeding timing T0 of the second sheet 11b than those described in the first embodiment.

[0098] For example, when a user sets a stack of sheets 11 in the paper feed tray 10 and inputs the sheet size to the operation panel 8, the user may mistakenly input a sheet size smaller than the size of the sheets 11 set in the paper feed tray 10. In this case, the sheet size setting unit 50 stores the sheet size 43 erroneously input by the user in the storage unit 41, so that when the paper feed control unit 52 sets the sheet interval according to the sheet size 43, the sheet interval during continuous paper feed is set based on the sheet size 43 smaller than the size of the sheets 11 actually accommodated in the paper feed tray 10. As a result, when a plurality of sheets 11 are continuously fed, for example, when the paper feed timing T0 for the second sheet 11b arrives, a situation may occur in which the trailing edge of the first sheet 11a has not yet passed the position of the paper feed sensor 18, and the paper feed sensor 18 is turned on at the paper feed timing T0 for the second sheet 11b.

[0099] FIG. 11 is a diagram showing a state in which the size of the first sheet 11a is larger than the set sheet size 43. When the size of the sheet 11a actually fed is larger than the sheet size 43 set by the user, when it is detected that it is time to feed the second sheet 11b, as shown in FIG. 11, the trailing edge of the first sheet 11a has not passed the position of the feed sensor 18, and the feed sensor 18 is still in the ON state. In this case, even if the feed control unit 52 starts the feed operation of the second sheet 11b, the feed sensor 18 switches from the ON state to the OFF state when the trailing edge of the first sheet 11a passes the position of the feed sensor 18, and then the feed sensor 18 switches from the OFF state to the ON state again when the leading edge of the second sheet 11b reaches the feed sensor 18. Therefore, the feed operation can be stopped at the position when the leading edge of the second sheet 11b reaches the position of the feed sensor 18.

[0100] However, when the feed sensor 18 is in the ON state at the feed timing T0 of the second sheet 11b, as described in the first embodiment, the feed control unit 52 cannot distinguish whether the ON state is due to the second sheet 11b being fed in multiple feedings when the first sheet 11a is fed, or due to the size of the first sheet 11a being larger than the set sheet size 43. Therefore, if a normal feed operation is performed, when the ON state is due to the second sheet 11b being fed in multiple feedings when the first sheet 11a is fed, as described in the first embodiment, the feed operation of the second sheet 11b cannot be temporarily stopped after the feed operation is started, and the sheet interval cannot be adjusted. Also, when the size of the first sheet 11a is larger than the set sheet size 43, it is preferable to detect it as a large size error and discharge a sheet 11a of a size different from the set sheet size 43.

[0101] Therefore, the image forming apparatus 1 of this embodiment performs the following process as a second sheet feeding operation (step S7) when the sheet feeding sensor 18 is in the on state when the sheet feeding timing T0 for the second or subsequent sheet 11b arrives.

[0102] FIG. 12 is a flowchart showing an example of a detailed processing procedure of the second sheet feeding operation (step S7) in the second embodiment. The flowchart shown in FIG. 12 is a process replacing the flowchart of FIG. 10 described in the first embodiment. When the sheet feeding control unit 52 starts the second sheet feeding operation (step S7) shown in FIG. 12, it resets the sheet feeding timing T2 (see FIG. 7) delayed by a predetermined time TP from the current timing T0 without starting the sheet feeding operation of the next sheet 11b (step S50). At this time, the sheet feeding control unit 52 continues the conveying operation of the previously fed sheet 11a. Then, the sheet feeding control unit 52 starts measuring time (step S51) and judges whether the reset sheet feeding timing T2 has arrived (step S52).

[0103] If it is not the reset feed timing T2 (NO in step S52), the feed control unit 52 determines whether the feed sensor 18 has changed to an OFF state in which the sheet 11 is not being detected (step S53). If the feed sensor 18 is still ON (NO in step S53), the process by the feed control unit 52 returns to step S52, and the process of determining whether it is the reset feed timing T2 is repeated.

[0104] If the paper feed sensor 18 has changed to the off state by the time of the reset paper feed timing T2 (YES in step S53), the paper feed control unit 52 determines that the previously fed sheet 11a has a large size error (step S54). Then, the paper feed control unit 52 continues the conveying operation of conveying the previously fed previous sheet 11a along the conveying path 14, and ejects it onto the paper output tray 6 (step S55). Thereafter, the job control unit 51 suspends the execution of the print job without feeding the next sheet 11b. It is preferable that, when the job control unit 51 ejects the previous sheet 11a and suspends the execution of the print job, the job control unit 51 displays on the display unit 8a that the sheet size 43 is incorrect, and prompts the user to reset the sheet size.

[0105] On the other hand, if the paper feed sensor 18 does not change to the OFF state and the reset paper feed timing T2 arrives (YES in step S52), the paper feed control unit 52 shortens the jam detection time to a predetermined time Tb that is shorter than that in the first paper feed operation (step S56), and starts the paper feed operation for the next sheet 11b (step S57).Then, the paper feed control unit 52 starts measuring time again (step S58).

[0106] Thereafter, the paper feed control unit 52 judges whether the time measured at step S58 has reached the predetermined time TP (step S59). That is, the paper feed control unit 52 judges whether the predetermined time TP has elapsed since the paper feed operation of the next sheet 11b was started. However, instead of the predetermined time TP, the paper feed control unit 52 may judge whether a predetermined time shorter than the predetermined time TP has elapsed. If the predetermined time TP has not elapsed since the paper feed operation of the next sheet 11b was started, the paper feed control unit 52 judges whether the paper feed sensor 18 has changed to an OFF state (step S60). As a result, if the paper feed sensor 18 is still in an ON state (NO in step S60), the process by the paper feed control unit 52 returns to step S59, and the process of judging whether the predetermined time TP has elapsed since the paper feed operation of the next sheet 11b was started is repeated.

[0107] If the paper feed sensor 18 changes to the OFF state before the predetermined time TP has elapsed since the start of the paper feed operation of the next sheet 11b (YES in step S60), the paper feed control unit 52 determines that the previously fed sheet 11a has a large size error (step S61). Then, the paper feed control unit 52 continues the transport operation of the previous sheet 11a previously fed and the next sheet 11b already fed, and discharges the previous sheet 11a and the next sheet 11b to the paper discharge tray 6 (step S62). However, this is not limited to this, and if the paper feed sensor 18 changes to the OFF state immediately after the start of the paper feed operation of the next sheet 11b, the paper feed operation of the next sheet 11b may be stopped and only the previous sheet 11a may be discharged to the paper discharge tray 6. Then, the job control unit 51 interrupts the execution of the print job. In this case, too, it is preferable that the job control unit 51, after ejecting the previous sheet 11a and the next sheet 11b and interrupting the execution of the print job, display the fact that the sheet size 43 is incorrect on the display unit 8a and prompt the user to reset the sheet size.

[0108] Furthermore, if the predetermined time TP has elapsed since the start of the feeding operation of the next sheet 11b without the paper feed sensor 18 changing to the off state (YES in step S59), the paper feed control unit 52 determines whether or not the next sheet 11b has been detected by the timing sensor 19 (step S63). If the next sheet 11b has not been detected by the timing sensor 19 (NO in step S63), the paper feed control unit 52 determines whether or not the time measurement started in step S58 has measured the predetermined time Tb (step S67).

[0109] If the timing sensor 19 detects the next sheet 11b before the predetermined time Tb has elapsed (YES in step S63), the feed control unit 52 temporarily stops the feed operation of the next sheet 11b with the leading edge of the next sheet 11b abutting against the nip of the timing roller 15 (step S64). Then, the feed control unit 52 waits until timing T6 (see FIG. 7) at which the toner image formed on the intermediate transfer belt 23 in the image forming unit 3 can be secondarily transferred to the sheet 11b (step S65), and when it detects that the timing T6 has been reached (YES in step S65), it rotates the timing roller 15 to resume the feed operation of the sheet 11b (step S66). This allows the toner image to be appropriately secondarily transferred to the sheet 11b.

[0110] On the other hand, if the predetermined time Tb has elapsed without the timing sensor 19 detecting the sheet 11b (YES in step S67), the sheet feed control unit 52 determines that a sheet feed jam has occurred when feeding the sheet 11b (step S68). In this case, the sheet feed control unit 52 stops the sheet feed operation of the sheet 11b (step S69). Then, the sheet feed control unit 52 causes the job control unit 51 to temporarily suspend the execution of the print job.

[0111] As described above, in the image forming apparatus 1 of the present embodiment, when a plurality of sheets 11 are continuously fed, if the sheet feed sensor 18 is already in an ON state detecting the sheet 11 when the sheet 11a previously fed reaches a predetermined position and the sheet feed timing T0 for feeding the next sheet 11b is reached, the process can be appropriately continued regardless of which of the two causes described above is the cause. For example, if the sheet feed sensor 18 is in an ON state due to the next sheet 11b being fed in multiple times while the previous sheet 11a is being fed, the same operation as in the first embodiment is performed, so that the interval between the previous sheet 11a and the next sheet 11b can be adjusted to a preset sheet interval and the print job can be continued. Also, if the size of the previous sheet 11a is larger than the set sheet size 43 and the sheet feed sensor 18 is in an ON state, the previous sheet 11a is determined to have a large size error, and the operation of discharging the sheet 11a with the large size error to the discharge tray 6 is continued, so that the job can be prevented from being interrupted with the sheet 11a with the large size error remaining in the conveying path 14.

[0112] In particular, the paper feed control unit 52 in this embodiment is configured to determine whether or not to perform the paper feed operation of the next sheet 11b at the reset paper feed timing T2 depending on the detection result of the paper feed sensor 18 during the period from when the paper feed timing of the next sheet 11b is reset to when the reset paper feed timing T2 occurs. Therefore, if the detection result of the paper feed sensor 18 changes during the period until the reset paper feed timing T2 occurs, it is possible to determine that there is a large size error and control not to perform the paper feed operation of the next sheet 11b, and if the detection result of the paper feed sensor 18 does not change during the period until the reset paper feed timing T2 occurs, it is possible to determine that there is no large size error and control to perform the paper feed operation of the next sheet 11b. Therefore, this is a configuration that can appropriately deal with each of the above two causes.

[0113] Incidentally, in this embodiment, the operations other than those described above are similar to those described in the first embodiment.

[0114] (Modification) Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible.

[0115] For example, in the above embodiment, the image forming apparatus 1 is an apparatus having only a print function, but is not limited to this. For example, the image forming apparatus 1 may be configured as an MFP (Multifunction Peripherals) having multiple functions such as a scan function and a copy function in addition to the print function.

[0116] In the above embodiment, the image forming apparatus 1 is a color machine capable of forming a color image. However, the image forming apparatus 1 is not limited to a color machine, and may be a monochrome dedicated machine. [Explanation of symbols]

[0117] 1. Image forming device 3 Image forming section (image forming means) 9. Controller 11(11a,11b,11c) Sheet 13 Paper feed roller (paper feeding means) 14 Transport Path 18 Paper feed sensor (sheet detection means) 51 Job control section 52 Paper feed control unit (paper feed control means) 53 Location management section (location management means)

Claims

1. A sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means and configured to detect a sheet; a sheet feed control means for resetting the sheet feed timing by the sheet feed means to a timing delayed by a predetermined time when the sheet detection means detects a sheet at the timing of the sheet feed means; Equipped with the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The image forming apparatus is characterized in that the paper feed control means does not cause the paper feed means to perform a sheet feed operation during the period from when the paper feed timing is reset to when the reset paper feed timing occurs, and determines whether or not to cause the paper feed means to perform a sheet feed operation at the reset paper feed timing depending on the detection result of the sheet detection means during the period from when the paper feed timing is reset to when the reset paper feed timing occurs.

2. A sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means and configured to detect a sheet; a sheet feed control means for resetting the sheet feed timing by the sheet feed means to a timing delayed by a predetermined time when the sheet detection means detects a sheet at the timing of the sheet feed means; Equipped with the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The image forming apparatus is characterized in that the paper feed control means does not cause the paper feed means to feed a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs, and if the sheet detection means continues to detect a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs, causes the paper feed means to start feeding a sheet at the reset paper feed timing.

3. A sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means and configured to detect a sheet; a sheet feed control means for resetting the sheet feed timing by the sheet feed means to a timing delayed by a predetermined time when the sheet detection means detects a sheet at the timing of the sheet feed means; Equipped with the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The image forming apparatus is characterized in that the paper feed control means does not cause the paper feed means to perform a sheet feed operation during the period from when the paper feed timing is reset to when the reset paper feed timing occurs, and if the sheet detection means changes to a state where it does not detect a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs, the image forming apparatus is characterized in that the paper feed control means does not cause the paper feed means to perform a sheet feed operation.

4. The image forming apparatus according to claim 2, characterized in that the sheet feeding control means, after starting the sheet feeding operation by the sheet feeding means, ejects the sheet fed by the sheet feeding means if the sheet detection means changes to a state in which it does not detect a sheet before the predetermined time has elapsed.

5. 5. The image forming apparatus according to claim 4, wherein the paper feed control means determines that the previous sheet is a large size error if the sheet detection means changes to a state where it does not detect a sheet before the specified time has elapsed after the paper feed means starts the sheet feed operation.

6. The image forming apparatus according to claim 3, characterized in that the paper feed control means determines that the previous sheet is a large size error if the sheet detection means changes to a state in which it does not detect a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs.

7. 7. The image forming apparatus according to claim 5, wherein when the paper feed control means determines that the previous sheet has a large size error, the paper feed control means continues the transport operation of the previous sheet in the sheet transport path and discharges the previous sheet from the sheet transport path.

8. an image forming means for generating an image to be transferred onto a sheet conveyed along the sheet conveying path, and for transferring the image onto the sheet when the sheet passes a predetermined transfer position; Further comprising:

8. The image forming apparatus according to claim 1, wherein the image forming unit starts an image generating operation at the same timing regardless of whether the paper feed timing is reset by the paper feed control unit.

9. a position management unit for managing position information of a sheet conveyed along the sheet conveying path; Further comprising: The image forming apparatus according to any one of claims 1 to 8, characterized in that when the sheet feeding operation by the sheet feeding means is started at the re-set sheet feeding timing, the position management means determines that the leading edge of the sheet is at the detection position by the sheet detection means, and updates the position information.

10. A sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means and configured to detect a sheet; A control method for an image forming apparatus comprising: a control step of resetting the sheet feed timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at the timing of sheet feed by the sheet feed means; Equipped with the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The control step is characterized in that it does not cause the paper feeding means to perform a sheet feeding operation during the period from when the paper feeding timing is reset to when the reset paper feeding timing occurs, and it determines whether or not to cause the paper feeding means to perform a sheet feeding operation at the reset paper feeding timing depending on the detection result of the sheet detection means during the period from when the paper feeding timing is reset to when the reset paper feeding timing occurs.

11. A sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means and configured to detect a sheet; A control method for an image forming apparatus comprising: a control step of resetting the sheet feed timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at the timing of sheet feed by the sheet feed means; Equipped with the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The control step is characterized in that it does not cause the paper feeding means to perform a sheet feeding operation during the period from when the paper feeding timing is reset to when the reset paper feeding timing occurs, and if the sheet detection means continues to detect a sheet during the period from when the paper feeding timing is reset to when the reset paper feeding timing occurs, it causes the paper feeding means to start a sheet feeding operation at the reset paper feeding timing.

12. A sheet feeding means for feeding a sheet toward a sheet transport path; a sheet detection means located downstream of the sheet feeding means and configured to detect a sheet; A control method for an image forming apparatus comprising: a control step of resetting the sheet feed timing to a timing delayed by a predetermined time when the sheet detection means detects a sheet at the timing of sheet feed by the sheet feed means; Equipped with the predetermined time is a time required for a sheet contained in a sheet feed tray and located at a predetermined reference position to be fed by the sheet feed means and to reach a detection position by the sheet detection means, The control step is characterized in that it does not cause the paper feeding means to perform a sheet feeding operation during the period from when the paper feeding timing is reset to when the reset paper feeding timing occurs, and if the sheet detection means changes to a state where it does not detect a sheet during the period from when the paper feeding timing is reset to when the reset paper feeding timing occurs, it does not cause the paper feeding means to perform a sheet feeding operation.

13. The control method according to claim 11, characterized in that the control step ejects the sheet fed by the sheet feeding means if the sheet detection means changes to a state in which it does not detect a sheet before the predetermined time has elapsed after the sheet feeding operation by the sheet feeding means has started.

14. The control method according to claim 13, characterized in that the control step determines that the previous sheet is a large size error if the sheet detection means changes to a state in which it does not detect a sheet before the specified time has elapsed after the sheet feeding operation by the sheet feeding means has started.

15. The control method according to claim 12, characterized in that the control step determines that the previous sheet is a large size error if the sheet detection means changes to a state in which it does not detect a sheet during the period from when the paper feed timing is reset to when the reset paper feed timing occurs.

16. 16. The control method according to claim 14, wherein, when it is determined that the previous sheet has a large size error, the control step continues the transport operation of the previous sheet in the sheet transport path and discharges the previous sheet from the sheet transport path.

17. The image forming apparatus includes: an image forming means for generating an image to be transferred onto a sheet conveyed along the sheet conveying path, and for transferring the image onto the sheet when the sheet passes a predetermined transfer position; Further comprising:

17. The control method according to claim 10, wherein the control step causes the image forming means to start an image forming operation at the same timing regardless of whether the paper feed timing is reset or not.

18. a position management step of managing position information of a sheet conveyed through the sheet conveying path; Further comprising: A control method according to any one of claims 10 to 17, characterized in that the position management step determines that the leading edge of the sheet is at the detection position detected by the sheet detection means when the sheet feeding operation by the sheet feeding means is started at the re-set feeding timing, and updates the position information.

Images