JP2019032453A - Image forming apparatus, sheet conveying method, and sheet conveying program - Google Patents

Abstract

To provide an image forming apparatus that, even when conveyance of sheets to an image transfer unit is stopped by timing adjustment means and a rear end part of a preceding sheet in a conveyance waiting state is present within a detection range of sheet detection means, can start feeding of a subsequent sheet earlier and confirm feeding of the sheets earlier, and in turn can start image formation on a transfer body earlier to improve productivity.SOLUTION: An image forming apparatus 1 confirms feeding of a sheet 400 before starting formation of a next image to a transfer body 201 performed by image formation means 211 to 214, and comprises control means 101 that, when conveyance of sheets to an image transfer unit 220 is stopped by timing adjustment means 330 and a rear end part 401 of the preceding sheet 400 in a conveyance waiting state is present within a detection range of sheet detection means 253, confirms feeding of a next subsequent sheet by feeding the subsequent sheet while avoiding a situation where the sheet detection means 253 cannot detect a leading end part of the subsequent sheet.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus such as a printer, a sheet conveying method and a sheet conveying program executed by the apparatus.

  In an image forming apparatus, it is a general method to increase the system speed in order to improve the productivity. However, since it leads to noise and cost increase, it is desired to improve the productivity while maintaining the system speed. ing. Here, as a method of improving productivity, a method of shortening the interval between the fed sheets has been proposed.

  For example, in Patent Document 1, when a sheet is transported from a sheet feeding cassette, the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are partially overlapped and sent, and only the succeeding sheet is stopped at a predetermined timing and the preceding sheet is There has been proposed a method of controlling the paper so that the sheet interval is slightly increased.

  Japanese Patent Application Laid-Open No. 2004-228688 calculates the sheet length of the fed sheet, calculates the sheet interval based on the calculated sheet length, and continues with the optimum sheet feeding timing based on the sheet length and the sheet interval. A method of starting paper feeding has been proposed.

  These are methods relating to control for improving productivity without increasing the system speed. However, as described below, productivity may not be improved even if these methods are used.

JP 2003-176045 A JP 11-59954 A

  That is, in an image forming apparatus having a mechanism in which the image forming path length of a transfer body such as an intermediate transfer belt for forming a transfer image is longer than the sheet conveying path length from the paper feed cassette to the image image transfer unit. It is necessary to match the leading edge of the image formed in the image image transfer unit with the leading edge of the paper, and the timing is determined by the path length and speed of the image forming / paper. In this case, in order to avoid wasteful consumption of toner in the image forming process, a method of starting image formation on the transfer body after confirming that the paper has been fed may be employed.

  In such an image forming apparatus, the time required to reach the paper image transfer unit is longer for the image on the transfer body than for the paper conveyance. There is a need to wait until it reaches a predetermined position. In addition, even in the case of continuous printing on a plurality of sheets, it is necessary to determine the paper feed for the subsequent paper, but in order to determine the paper feed, the trailing edge of the preceding paper is the paper After passing through the detection sensor, the leading edge of the subsequent sheet needs to reach the sheet detection sensor. In this case, the leading paper is stopped by the registration roller unit and waiting for the leading edge of the image to reach a predetermined position, and the trailing edge of the preceding paper remains within the detection range of the paper detection sensor. In this case, the succeeding sheet cannot be fed until the preceding sheet starts to be conveyed to the image transfer unit and the trailing end of the sheet passes the detection range of the sheet detection sensor. For this reason, it is necessary to delay the feeding timing of the succeeding sheet, and as a result, the confirmation that the succeeding sheet has been fed is delayed, and the start of image formation on the transfer body is delayed, resulting in poor productivity. there were.

  The present invention has been made in view of such a technical background, and the trailing edge of the preceding sheet waiting for conveyance is detected by the sheet detection unit when the conveyance to the image transfer unit is stopped by the timing adjustment unit. The image forming apparatus and the paper that can improve the productivity by starting the feeding of the succeeding paper early and confirming the paper feeding early, and by extension, starting the image formation on the transfer body. It is an object to provide a conveyance method and a sheet conveyance program.

The above problem is solved by the following means.
(1) A paper feed roller pair for feeding paper from the paper feed unit, a paper detection unit for detecting paper fed from the paper feed unit by the paper feed roller pair, an image imaging unit, and the image production unit A transfer body on which an image is formed by the image means; a transfer means for transferring an image formed on the transfer body onto a paper fed by the paper feed means at an image transfer portion; and a paper by the transfer means In order to adjust the transfer timing of the image to the image transfer unit, and a timing adjustment unit that temporarily stops the conveyance of the sheet to the image transfer unit. In the image forming apparatus that starts image formation, when the trailing edge of the preceding sheet waiting for conveyance is present in the detection range of the sheet detection unit due to the conveyance stop to the image transfer unit by the timing adjustment unit , The paper detection An image forming apparatus, comprising: a control unit configured to confirm feeding of the succeeding sheet by feeding the succeeding sheet while avoiding a state in which the leading edge of the succeeding sheet cannot be detected. .
(2) The timing adjusting means includes a pair of registration rollers, and a first roller pair for forming a first loop on the sheet between the registration roller pair on the upstream side of the registration roller pair in the sheet conveyance direction. And at least one second roller pair for forming a second loop on the sheet on the upstream side of the first roller pair, and the control means includes the first roller by the second roller pair. By forming at least one second loop on the upstream side of the pair and retracting the trailing edge of the preceding sheet waiting for conveyance from the detection range of the sheet detection unit, the sheet detection unit causes the subsequent sheet 2. The image forming apparatus according to item 1, wherein a state in which the leading end of the sheet cannot be detected is avoided.
(3) A retracting means for retracting the trailing edge of the preceding sheet waiting for transport from the detection range of the sheet detecting means is provided in a sheet transport path in the vicinity of the sheet detecting means, and the control means 2. The image forming apparatus according to claim 1, wherein the sheet detecting unit avoids a state in which the leading end portion of the succeeding sheet cannot be detected by operating the retracting unit.
(4) The torque force of each roller pair is the registration roller pair> first roller pair> second roller pair> feed roller pair, and the force that the second loop attempts to return to <the second roller pair 3. The image forming apparatus according to item 2, which is set to a torque force.
(5) The image forming apparatus according to (2) or (4), wherein the first loop and at least one second loop are formed in order from the downstream side in the paper transport direction.
(6) Loop amount detection means for detecting the loop amount of the second loop is provided, and the control means is at least waiting for conveyance when the loop amount of the second loop detected by the loop amount detection means is at least 6. The preceding item 2, 4 or 5, wherein the second loop is formed so that the trailing edge of the preceding sheet has a loop amount necessary to pass through the detection range of the sheet detection means. Image forming apparatus.
(7) A plurality of second roller pairs are provided on the upstream side of the first roller pair, and a plurality of second loops can be formed between the roller pairs. 7. The image forming apparatus according to any one of items 2 and 4 to 6, wherein one or a plurality of second loops are formed according to the length.
(8) The interval between each pair of rollers capable of forming the second loop includes different ones, and the control means determines the distance between the pair of rollers forming the second loop according to the length of the sheet to be conveyed. 8. The image forming apparatus according to item 7, which is selected.
(9) The control means is configured so that the second loop forms the second loop only when the trailing edge of the preceding paper waiting for conveyance can retract the detection range of the paper detection means. 9. The image forming apparatus according to any one of items 2 and 4 to 8 above.
(10) Even if the rear end portion of the preceding sheet waiting for conveyance cannot retract the detection range of the sheet detection unit due to the formation of the second loop, the control unit may The image forming apparatus according to any one of the preceding items 2, 4 to 9, wherein the two loops are formed.
(11) The image forming apparatus according to any one of (2), (4) to (10), wherein the control unit forms the second loop when the preceding sheet is conveyed to the registration roller pair.
(12) The control means drives the second roller pair on the upstream side to drive the second roller pair on the upstream side with respect to the preceding sheet waiting for conveyance due to the conveyance stop to the image transfer unit by the registration roller pair. 12. The image forming apparatus according to any one of items 2 and 4 to 11 described above.
(13) The control unit is configured to form the second loop when the conveyance of the preceding sheet waiting for conveyance to the image transfer unit is started due to the conveyance stop of the registration roller pair to the image transfer unit. The image forming apparatus according to any one of 4 to 12.
(14) The control means forms the second loop by providing a difference in conveying speed between the downstream roller pair and the upstream second roller pair, and the second loop with the target loop amount. 14. The image forming apparatus as described in 11 or 13 above, wherein the difference in the conveyance speed between the downstream roller pair and the upstream second roller pair is eliminated.
(15) The image forming apparatus according to (13), wherein the control unit forms the second loop by accelerating the start timing of the upstream second roller pair relative to the downstream roller pair.
(16) The image forming apparatus according to item 11, wherein the control unit stops the downstream roller pair earlier than the upstream second roller pair to form the second loop.
(17) The image forming apparatus according to (3), wherein the retracting unit is a unit that retracts the trailing end of the sheet from the sheet conveying path by opening a sheet conveying path in the vicinity of the sheet detecting unit.
(18) A plurality of the sheet detection means are provided, and switching means for switching the conveyance path of the sheet passing through each of the sheet detection means for each sheet detection means is provided. The control means conveys the sheet by the switching means. 4. The image forming apparatus according to item 1 or 3, wherein the sheet detection unit avoids a state in which the leading end portion of the succeeding sheet cannot be detected by switching the path.
(19) A pair of paper feed rollers that feed paper from the paper feed unit, a paper detection unit that detects paper fed from the paper feed unit by the pair of paper feed rollers, an image forming unit, and the image forming unit A transfer body on which an image is formed by the image means; a transfer means for transferring an image formed on the transfer body onto a paper fed by the paper feed means at an image transfer portion; and a paper by the transfer means In order to adjust the transfer timing of the image to the image transfer unit, and a timing adjustment unit that temporarily stops the conveyance of the sheet to the image transfer unit. When the image forming apparatus that starts image formation has a trailing edge of a preceding sheet waiting for conveyance due to the conveyance stop to the image transfer unit by the timing adjustment unit within the detection range of the sheet detection unit , The paper detection means By feeding the succeeding sheet to avoid a situation that can not detect the leading end of the next following sheet, the sheet conveying method characterized by performing a control step of determining the feeding of the following sheet.
(20) A paper feed roller pair for feeding paper from the paper feed unit, a paper detection unit for detecting paper fed from the paper feed unit by the paper feed roller pair, an image imaging unit, and the image production unit A transfer body on which an image is formed by the image means; a transfer means for transferring an image formed on the transfer body onto a paper fed by the paper feed means at an image transfer portion; and a paper by the transfer means In order to adjust the transfer timing of the image to the image transfer unit, and a timing adjustment unit that temporarily stops the conveyance of the sheet to the image transfer unit. In the computer of the image forming apparatus that starts image formation, the trailing edge of the preceding sheet waiting for conveyance due to the conveyance stoppage to the image transfer unit by the timing adjustment unit exists in the detection range of the sheet detection unit. When the front By sheet detection means for feeding said subsequent sheet to avoid a situation that can not detect the leading end of the next following sheet, the sheet conveying program for executing a control step of determining the feeding of the following sheet.

  According to the invention described in (1) above, when the trailing edge of the preceding sheet waiting for conveyance is present in the detection range of the sheet detection unit due to the conveyance stop to the image transfer unit by the timing adjustment unit such as the registration roller pair. Since the paper detection means determines the paper feeding by feeding the succeeding paper while avoiding the state where the leading edge of the next succeeding paper cannot be detected, the trailing edge of the preceding paper waiting for conveyance Is in the detection range of the paper detection means, the feeding of the subsequent paper can be started early and the paper feed can be confirmed at an early stage. Can be improved.

  According to the invention described in (2) above, the first roller pair for forming the first paper loop between the registration roller pair is provided on the upstream side of the registration roller pair that is the timing adjusting means, and A second roller pair is provided on the upstream side of the first roller pair, and the second roller pair forms at least one second loop on the sheet on the upstream side of the first roller pair, so that the preceding sheet waiting for conveyance Since the trailing edge is retracted from the detection range of the paper detection means, a state in which the paper detection means cannot detect the leading edge of the succeeding paper can be reliably avoided by a relatively simple method.

  According to the invention described in (3), the retracting means for retracting the trailing edge of the preceding sheet waiting for transport from the detection range of the sheet detecting means provided in the sheet transport path in the vicinity of the sheet detecting means. By operating, it is possible to reliably avoid a state in which the paper detection means cannot detect the leading edge of the subsequent paper.

  According to the invention described in item (4) above, the torque force of each roller pair is: registration roller pair> first roller pair> second roller pair> feed roller pair, and the second paper loop is based on Since the force to return <the torque force of the second roller pair is set, the second loop can be reliably formed while properly conveying the paper by each roller pair.

  According to the invention described in item (5) above, the first loop and the at least one second loop are formed in order from the downstream side in the paper transport direction, so the upstream loop affects the downstream loop. Therefore, the trailing edge of the preceding paper waiting for conveyance can be reliably retracted from the detection range of the paper detection means.

  According to the invention described in item (6), the loop amount of the second loop detected by the loop amount detection unit is such that at least the trailing edge of the preceding sheet waiting for conveyance passes the detection range of the sheet detection unit. Since the second loop is formed so as to have a loop amount necessary for this, it is possible to reliably avoid a state in which the paper detection means cannot detect the leading edge of the next succeeding paper.

  According to the invention described in item (7), one or a plurality of second loops can be formed according to the length of the sheet to be conveyed. It can be surely retracted from the detection range of the detection means.

  According to the invention described in item (8), the distance between each pair of rollers capable of forming the second loop includes different ones, and the roller that forms the second loop according to the length of the sheet to be conveyed Since the pair is selected, the second loop can be formed at a position where the load on the sheet due to the formation of the second loop is small.

  According to the invention described in the preceding item (9), the second loop is formed only when the trailing edge of the preceding sheet waiting for conveyance can retreat the detection range of the sheet detection unit by forming the second loop. Therefore, it is possible to prevent an unnecessary load on the paper due to the formation of the second loop.

  According to the invention described in item (10) above, even if the trailing edge of the preceding paper waiting for conveyance cannot be retracted from the detection range of the paper detection means by the formation of the second loop, Since the second loop is formed in advance, the trailing edge of the sheet passes the detection range when the sheet waiting for conveyance is resumed by driving the registration roller pair. Time can be shortened and it contributes to efficiency improvement.

  According to the invention described in item (11) above, since the second loop is formed when the preceding sheet is conveyed to the registration roller pair, the second loop can be formed early, and image formation starts accordingly. Can be accelerated and productivity can be improved.

  According to the invention described in item (12), the second roller pair on the upstream side is driven with respect to the preceding sheet waiting for conveyance due to the conveyance stop to the image transfer unit by the registration roller pair. Since the second loop is formed, the formation of the second loop can be delayed, and the load on the paper due to the formation of the second loop can be reduced. Moreover, since the registration roller pair is not driven, the second loop can be formed accurately.

  According to the invention described in item (13) above, the second loop is formed when the conveyance of the preceding sheet waiting for conveyance to the image transfer unit is started due to the conveyance stop to the image transfer unit by the pair of registration rollers. The formation of the second loop can be further delayed, and the load on the paper due to the formation of the second loop can be minimized.

  According to the invention described in the preceding item (14), the second loop is formed by providing a difference in conveyance speed between the downstream roller pair and the upstream second roller pair, and the second loop pair is formed with the target loop amount. After the two loops are formed, the conveyance speed difference between the downstream roller pair and the upstream second roller pair is eliminated, so that the second loop can be reliably formed.

  According to the invention described in the above item (15), the second loop can be reliably formed by making the start timing of the upstream second roller pair earlier than the downstream roller pair.

  According to the invention described in item (16) above, the second loop can be reliably formed by stopping the downstream roller pair earlier than the upstream second roller pair.

  According to the invention described in the preceding item (17), the rear end portion of the sheet can be reliably retracted from the sheet conveying path by opening the sheet conveying path in the vicinity of the sheet detecting means.

  According to the invention described in the above item (18), by switching the paper transport path, it is possible to avoid a state in which the paper detection unit cannot detect the leading edge of the subsequent paper.

  According to the invention described in the preceding item (19), even if the trailing edge of the preceding paper waiting for conveyance is in the detection range of the paper detection means, the feeding of the subsequent paper is started early and is fed. Paper determination can be performed at an early stage, and as a result, the start of image formation on a transfer body can be accelerated and productivity can be improved.

  According to the invention described in the preceding item (20), even if the trailing edge of the preceding paper waiting for conveyance is in the detection range of the paper detection means, the feeding of the subsequent paper is started early and is fed. It is possible to cause the computer of the image forming apparatus to execute processing that can determine the paper at an early stage, and thus improve the productivity by starting the image formation on the transfer body earlier.

FIG. 2 is a diagram illustrating a schematic configuration of a sheet conveyance path in an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus. FIG. 6 is a schematic configuration diagram of a conveyance path for paper fed from a manual feed tray. 6 is a flowchart illustrating a conventional sheet conveyance control process from when a sheet 400 is fed from a manual feed tray 250 until it is conveyed to a registration roller pair 330. 6 is a flowchart illustrating a conventional paper transport process when continuously printing on a plurality of paper sheets. FIG. 10 is a diagram for explaining a state in which a rear end portion of a front sheet is retracted from a detection range of a manual sheet feed sensor by forming a second loop on the front sheet. It is a figure for demonstrating the state which can form two or more 2nd loops. 6 is a flowchart illustrating a conveyance process when the rear end portion of a front sheet is retracted from a detection range of a manual sheet feed sensor. (A) (B) is a figure for demonstrating other embodiment of this invention. (A) (B) is a figure for demonstrating other embodiment of this invention. It is a timing chart in the conventional paper conveyance. 6 is a timing chart in paper conveyance according to the present embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a sheet conveyance path in an image forming apparatus according to an embodiment of the present invention.

  In FIG. 1, reference numeral 201 denotes an endless intermediate transfer belt as a transfer member, and this intermediate transfer belt 201 is driven and conveyed in a fixed direction by a driving roller 201a and a driven roller 201b.

  Four photosensitive drums 211 a to 214 a for forming toner images of respective colors of Y (yellow), M (magenta), C (cyan), and K (black) are provided along the conveyance path of the intermediate transfer belt 201. The image forming units 211 to 214 are sequentially arranged. Then, by passing the image formed by each of the image forming units 211 to 214 and transferred onto the intermediate transfer belt 201 through the secondary transfer roller pair 221 disposed in the image transfer unit 220, the secondary transfer roller is similarly used. The sheet is transferred onto the sheet in a superimposed manner with the sheet passing through the pair 221.

  In addition, the upper and lower paper feed cassettes 230 and 240 are provided on the upper and lower sides, and the paper stored in the upper paper feed cassette 230 is taken out from the paper feed cassette 230 by the pickup roller 231 and vertically fed by the first-stage paper feed roller pair 232. The paper is fed to the transport path, and further fed to the paper transport path 300 arranged horizontally by the first-stage vertical transport roller pair 233 provided in the vertical transport path. On the other hand, the paper stored in the lower paper feed cassette 240 is similarly taken out from the paper feed cassette 240 by the pickup roller 241 and fed to the vertical transport path by the second-stage paper feed roller pair 242, and further the vertical transport path. The sheet is fed to a sheet conveyance path 300 arranged horizontally by a second-stage vertical conveyance roller pair 243 provided on the sheet. A first-stage paper feed sensor 234 and a second-stage paper feed sensor 234 for detecting paper fed from the paper feed cassettes 230 and 240 are provided on the exit side of the pair of paper feed rollers 232 and 242 of the upper and lower paper feed cassettes 230 and 240. A paper feed sensor 244 is provided.

  Further, in this embodiment, a manual feed tray 250 is provided, and the paper set on the manual feed tray 250 is taken in by the pickup roller 251 and fed to the paper feed path 300 by the paper feed roller pair 252. It has become. Note that a manual paper feed sensor 253 that detects paper fed from the manual feed tray 250 is provided on the exit side of the pair of paper feed rollers 252 of the manual feed cassette 250.

  Further, a second loop forming roller pair 310 is disposed on the paper conveyance path 300 continuing from the manual feed tray 250, and the first loop forming roller pair 320 is disposed downstream of the second loop forming roller pair 310. , And the sheet fed and conveyed from the upper sheet cassette 230 and the lower sheet cassette 240 is conveyed between the first loop forming roller pair 320 and the second loop forming roller pair 310. It joins the path 300.

  A registration roller pair 330 is disposed between the first loop forming roller pair 320 and the image transfer unit 220 in the paper conveyance path 300, and to the registration roller pair 330 on the upstream side of the registration roller pair 330. A registration sensor 340 for detecting the conveyed paper is disposed.

  The registration roller pair 330 is based on the sheet detection result of the registration sensor 340 in order to adjust the timing at which the image formed on the intermediate transfer belt 201 is transferred to the sheet by the secondary transfer roller pair 221 in the image transfer unit 220. Thus, it serves to temporarily stop the conveyance of the sheet to the image transfer unit 220. The first loop forming roller pair 320 forms a first loop on the sheet between the registration roller pair 330 and the first loop forming roller pair 320, and the second loop forming roller pair 310 is a manual feed. A second loop is formed on the paper between the first loop forming roller pair 320 and the second loop forming roller pair 310 with respect to the paper fed from the tray 250. Will be described later.

  The sheet on which the image is transferred by the image transfer unit 220 is fixed while passing through the fixing roller pair 350, and is discharged to a discharge tray (not shown) by the discharge roller pair 360. A paper discharge sensor 370 that detects paper to be discharged is provided on the upstream side of the paper discharge roller pair 360.

  FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus.

  As shown in FIG. 2, the image forming apparatus 1 includes a control unit 100, a fixed storage device 110, an image reading device 120, an operation panel 130, an image output device 140, a printer controller 150, a network interface (network I / F) 160, wireless A communication interface (wireless communication I / F) 170, an authentication unit 180, and the like are provided, and are connected to each other via a system bus 175.

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, an S-RAM (Static Random Access Memory) 103, an NV-RAM (Non Volatile RAM) 104, a clock IC 105, and the like.

  The CPU 101 performs overall control of the entire image forming apparatus 1 by executing an operation program stored in the ROM 102 or the like. For example, control is performed so that a copy function, a printer function, a scan function, a facsimile function, and the like can be executed. In particular, in this embodiment, paper conveyance control or the like is performed at the time of copying or printing at the time of image formation on the paper executed by the image output apparatus. Details will be described later.

  The ROM 102 stores programs executed by the CPU 101 and other data.

  The S-RAM 103 serves as a work area when the CPU 101 executes a program, and temporarily stores a program, data when the program is executed, and the like.

  The NV-RAM 104 is a non-volatile memory backed up by a battery, and stores various settings and information related to image formation.

  The clock IC 105 measures time and functions as an internal timer to measure processing time.

  The fixed storage device 110 includes a hard disk or the like, and stores programs, various data, and the like.

  The image reading device 120 includes a scanner unit as an imaging unit, scans an original set on a platen glass, and converts an image of the read original into image data that is an electrical signal.

  The operation panel 130 is used when a user gives a job instruction or various settings to the image forming apparatus 1, and includes a reset key 131, a start key 132, a stop key 133, a display unit 134, a touch panel 135, and the like. ing.

  The reset key 131 is used when resetting the setting, the start key 132 is used for a start operation such as scanning, and the stop key 133 is pressed when the operation is interrupted. It is.

  The display unit 134 is composed of, for example, a liquid crystal display device and displays messages, various operation screens, and the like. The touch panel 135 is formed on the screen of the display unit 134 and detects a user's touch operation.

  The image output device 140 prints on a sheet a copy image generated from image data of a document read by the image reading device 120 or print data transmitted from an external terminal device or the like, and outputs it as a printed matter. .

  The printer controller 150 generates a copy image from print data received by the network interface 160.

  The network I / F 160 functions as a communication unit that transmits / receives data to / from an external device such as a user terminal via the network 4, and the wireless communication I / F 170 communicates with the external device by short-range wireless communication. Interface.

  The authentication unit 180 acquires authentication information for a logged-in user, and performs authentication by comparing the authentication information with verification information stored in the fixed storage device 110 or the like in advance. Note that comparison / collation between the user authentication information and the collation information may be performed by an external authentication server, and authentication may be performed by the authentication unit 180 receiving an authentication result from the authentication server.

  FIG. 3 is a schematic configuration diagram of a conveyance path of a sheet fed from the manual feed tray 250, and shows a configuration from the manual feed roller pair 252 to the registration roller pair 330 among the configurations shown in FIG. The registration sensor 340 is omitted.

  As shown in FIG. 3, the paper 400 set on the manual feed tray 250 is fed onto the paper transport path 300 by the manual paper feed roller pair 252 and detected by the manual paper feed sensor 253. When the paper feed sensor 253 detects the paper 400, it is determined that the paper is fed from the manual feed tray 250. After confirming that the sheet feeding has been performed, the image forming units 211 to 214 start image formation (image forming) on the intermediate transfer belt 201.

  The sheet 400 that has passed through the manual sheet feed sensor 253 passes through the second loop forming roller pair 310 and the first loop forming roller pair 320 and is conveyed to the registration roller pair 330. Then, in order to register the registration of the top of the image formation image with the top of the sheet 400, the rotational driving of the registration roller pair 330 is stopped to stop the sheet 400 and wait. Further, in order to correct the skew of the sheet 400, the first loop forming roller pair 320 forms a first loop 410 on the sheet 400 between the registration roller pair 330 and the first loop forming roller pair 320. . When the synchronization timing by the paper registration comes, the registration roller pair 330 is driven to start conveying the standby paper 400 to the image transfer unit 220 formed in the nip portion of the secondary transfer roller pair 221. The paper is discharged through a known image transfer process.

  FIG. 4 is a flowchart showing a conventional sheet conveyance control process until the sheet 400 is fed from the manual feed tray 250 and conveyed to the registration roller pair 330 as described above. The processing shown in the flowcharts shown in FIG. 4 and FIG. 5 and thereafter is executed by the CPU 101 of the image forming apparatus 1 operating according to an operation program stored in the ROM 102 or the like.

  In step S01, paper is fed from the manual feed tray 250. By this paper feed, the manual paper feed sensor 253 detects the paper 400 and is turned on to confirm the paper feed. Image formation on the intermediate transfer belt 201 is started by each of the image forming units 211 to 214 when paper feeding is confirmed. In step S <b> 02, the fed paper 400 is conveyed to the registration roller pair 330. In step S03, the driving of the registration roller pair 330 is stopped to wait for the sheet 400 (waiting for image registration), and the sheet between the registration roller pair 330 and the first loop forming roller pair 320 is corrected for skew correction. 400 causes a first loop 410 to be formed.

  Next, in step S04, it is determined whether or not waiting for image registration is completed. If it is not completed (NO in step S04), the process waits for completion in step S04. If the image registration wait is completed (YES in step S04), the process is terminated, but the sheet 400 is conveyed to the image transfer unit 220 by driving the registration roller pair 330.

  FIG. 5 is a flowchart showing a conventional paper conveyance process when continuously printing on a plurality of paper sheets.

  In step S11, it is checked whether or not there is a preceding sheet (preceding sheet) 400. If not (NO in step S11), the process proceeds to step S13. If the front paper 400 is present (YES in step S11), whether or not the front paper 400 has the manual paper feed sensor 253 turned on in step S12, in other words, the rear edge of the front paper 400 is the manual paper feed sensor 253. Find out if you are missing. If the front paper 400 has the manual paper feed sensor 253 turned on (YES in step S12), the rear end portion 401 of the front paper 400 has not yet passed through the manual paper feed sensor 253, so that the process waits in step S12. The paper 400 turns off the manual paper feed sensor 253, that is, waits for the rear end portion 401 of the front paper 400 to pass through the manual paper feed sensor 253. If the front paper 400 does not turn on the manual paper feed sensor 253 (NO in step S12), the rear end portion 401 of the front paper 400 passes through the manual paper feed sensor 253, and the front paper 400 has already entered the image transfer unit 220. Since it is being conveyed, the process proceeds to step S13.

  In step S13, the next sheet (following sheet) is fed from the manual feed tray 250. By this sheet feeding, the manual sheet feeding sensor 253 is turned on by the succeeding sheet, and the sheet feeding is determined. Image formation on the intermediate transfer belt 201 is started by each of the image forming units 211 to 214 when paper feeding is confirmed. In step S <b> 14, the fed paper is conveyed to the registration roller pair 330. In step S15, the driving of the registration roller pair 330 is stopped to wait for the paper (waiting for image registration), and the paper is placed between the registration roller pair 330 and the first loop forming roller pair 320 for skew correction. A first loop is formed.

  Next, in step S16, it is determined whether waiting for image registration is completed. If not completed (NO in step S16), the process waits for completion in step S04. If the image registration waiting is completed (YES in step S 16), the process is terminated, but the sheet is conveyed to the image transfer unit 220 by driving the registration roller pair 330.

  In the processing shown in the flowchart of FIG. 5, the front paper 400 turns off the manual paper feed sensor 253, that is, waits for the rear end 401 of the front paper 400 to pass through the manual paper feed sensor 253, and feeds the subsequent paper. However, even if the front paper 400 does not wait for the manual paper feed sensor 253 to turn off, the succeeding paper reaches the manual paper feed sensor 253 after the rear end portion 401 of the front paper 400 passes through the manual paper feed sensor 253. The subsequent paper may be started to be fed at such timing.

  However, if the front sheet (preceding sheet) 400 is in the standby state with the registration roller pair 330 while the manual sheet feeding sensor 253 is turned on at the rear end 401, the succeeding sheet cannot be fed. Since the manual paper feed sensor 253 is not turned on, the feeding of the subsequent paper is not confirmed. Therefore, as in the present embodiment, when the image forming path length of the intermediate transfer belt 201 on which the transfer image is formed is longer than the sheet conveying path length from the manual feed tray 250 to the image transfer unit 220, Although the image formation of the paper can be started, the image formation is not started because the paper feed is not confirmed, and thus the productivity is lowered.

  Therefore, in this embodiment, as shown in FIG. 6, the second loop 420 is formed on the front sheet 400 between the first roller pair 320 and the second roller pair 310 provided on the upstream side thereof. The rear end portion 401 of the paper 400 is retracted from the detection range of the manual paper feed sensor 253, that is, the rear end portion 401 of the front paper 400 is removed from the manual paper feed sensor 253, and the manual paper feed sensor 253 is forcibly turned off. Then, control is performed so that the subsequent sheet can be fed. When the feeding of the succeeding sheet is started and the manual sheet feeding sensor 253 is turned on, the feeding of the succeeding sheet is confirmed, so that the preceding sheet 400 is transferred to the succeeding sheet even when waiting on the registration roller pair 330. Image formation is started and the start of image formation can be accelerated, thereby improving productivity.

  Here, the amount of the second loop 420 may be an amount sufficient for the trailing edge 401 of the front paper 400 to pass through the manual paper feed sensor 253. The amount of the second loop 420 may be measured by providing a pressure sensor (not shown) so as to be able to come into contact with the loop portion of the front sheet 400 and measuring the pressure of the loop portion with this pressure sensor. Further, the amount of the second loop 420 is set in advance according to the paper size without measuring the amount of the second loop 420, and the second loop 420 is set so as to correspond to the paper size. It may be formed.

  Further, as shown in FIG. 7, a plurality of second loops 420 can be formed by arranging a plurality of second roller pairs 311 and 312 at an interval on the upstream side of the first roller pair 320. One or a plurality of second loops 420 may be formed according to the length of the front sheet 400 to be conveyed. For example, in the case of a long sheet, if the trailing end 401 of the sheet 400 cannot be retracted from the detection range of the manual sheet feed sensor 253 by forming only one second loop 420, as shown in FIG. Two or more second loops 420 may be formed. In addition, the distance between the first roller pair 320 and the second roller pair 311 closest to the upstream side and the distance between the second roller pairs 311 and 312 are set to different distances according to the length of the front sheet 400. Thus, the pair of rollers forming the second loop 420 may be selected.

  Here, the first loop 410 for cue correction formed on the front sheet 400 between the registration roller pair 330 and the first roller pair 320, the first roller pair 320 and the second roller pair 311 closest to the upstream side. The second loop 420 formed between (310) and the second loop 420 formed between each pair of second rollers 311 and 312 on the upstream side thereof is downstream in the sheet conveying direction. The first loop 410 on the side is formed in order, and the upstream loop does not affect the downstream loop, and the rear end portion 401 of the front sheet 400 waiting for conveyance is moved by the manual feed sensor 253. This is desirable in that it can be reliably retracted from the detection range.

  Further, the torque force of each roller pair is set such that the registration roller pair 330> the first roller pair 320> the second roller pair 310> the paper feed roller pair 252. This is desirable because it can be done. In addition, the force that the second loop 420 tries to return to <the torque force of the second roller pair 310, 311 and 312 is set while appropriately transporting the front sheet 400 by each roller pair. This is desirable in that the second loop 420 can be reliably formed.

  The timing of forming the second loop 420 may be when the front sheet 400 is waiting for image registration by the registration roller pair 330 or when it is transported to the registration roller pair 330 or at the time of entry. Alternatively, it may be at the start of conveyance of the front sheet 400 waiting for conveyance by the registration roller pair 330 to the image transfer unit 220.

  In the case where the second loop 420 is formed when the front sheet 400 is conveyed to the registration roller pair 330, the second loop 420 can be formed at an early stage, so that the start of image formation can be accelerated and the productivity can be increased. Can be improved. In this case, the second loop 420 is formed by providing a conveyance speed difference between the downstream roller pair 320, 311 and the upstream second roller pair 310, 311, 312, and the target loop amount is set. After the second loop 420 is formed, the conveyance speed difference between the downstream roller pair 320, 311 and the upstream second roller pair 310, 311, 312 may be eliminated. Alternatively, the second loop 420 may be formed by stopping the downstream roller pair 320, 311 earlier than the upstream second roller pair 310, 311, 312.

  In addition, when the second loop 420 is formed on the previous sheet 400 waiting for conveyance due to the conveyance stop to the image transfer unit 220 by the registration roller pair 330, the formation of the second loop 420 can be delayed. The load on the front sheet 400 due to the formation of the second loop 420 can be reduced. In addition, since the registration roller pair 330 and the like are not driven, the second loop 420 can be accurately formed. In this case, the second loop 420 may be formed by driving the upstream second roller pair 310, 311, 312 with respect to the front sheet 400 waiting for conveyance by the registration roller pair 330.

  When the second loop 420 is formed at the start of conveyance of the front sheet 400 waiting for conveyance due to the conveyance of the registration roller pair 330 to the image transfer unit 220 to the image transfer unit 220, the second loop 420 is formed. Can be further delayed, and the load on the front sheet 400 due to the formation of the second loop 420 can be minimized. In this case, the second loop may be formed by accelerating the start timing of the upstream second roller pair 310, 311, 312 relative to the downstream roller pair.

  Further, the second loop 420 is formed only when the rear end portion 401 of the front sheet 400 waiting to be conveyed can retract the detection range of the manual sheet feed sensor 253 by forming the second loop 420. Also good. Since the second loop 420 is not formed when the rear end portion 401 of the front sheet 400 waiting for conveyance cannot be retracted from the detection range of the manual sheet feed sensor 253 due to the formation of the second loop 420, the second loop 420 is not formed. By forming the loop 420, it is possible to prevent a wasteful load from being applied to the sheet 400.

  On the other hand, even if the rear end portion 401 of the front paper 400 waiting for conveyance cannot be retracted from the detection range of the manual paper feed sensor 253 even when the second loop 420 is formed, the second paper is added to the front paper 400. The loop 420 may be formed. In this case, by forming the second loop 420 in advance, the trailing edge 401 of the sheet passes the detection range when the conveyance of the front sheet 400 waiting for conveyance is resumed by driving the registration roller pair 330. This shortens the time required to improve efficiency.

  FIG. 8 is a flowchart illustrating a conveyance process when the trailing edge 401 of the front sheet 400 is retracted from the detection range of the manual sheet feed sensor 253.

  In step S21, paper is fed from the manual feed tray 250. By this paper feed, the manual paper feed sensor 253 detects the paper 400 and is turned on to confirm the paper feed. Image formation on the intermediate transfer belt 201 is started by each of the image forming units 211 to 214 when paper feeding is confirmed. In step S 22, the fed paper 400 is conveyed to the registration roller pair 330. In step S23, the driving of the registration roller pair 330 is stopped and the sheet 400 is waited (waiting for image registration). 400 causes a first loop 410 to be formed.

  Next, in step S24, it is checked whether or not there is a next sheet (subsequent sheet). If not (NO in step S24), the process proceeds to step S25. If there is a next sheet (YES in step S24), it is checked in step S26 whether the own sheet (previous sheet) has the manual sheet feed sensor 253 turned on. If it is not on (NO in step S26), the process proceeds to step S25. If it is on (YES in step S26), in step S27, the second loop 420 is formed to retract the paper trailing edge 401 from the detection range of the manual paper feed sensor 253, and then the process proceeds to step S25. By forming the second loop 420 and retracting the rear end 401 of the front paper 400 from the detection range of the manual paper feed sensor 253, the next paper (subsequent paper) can be fed and the manual paper feed sensor 253 can be fed. Turn on. When the manual paper feed sensor 253 is turned on, the feeding of the next paper is confirmed, and image formation on the intermediate transfer belt 201 by the image forming units 211 to 214 is started.

  In step S25, it is determined whether waiting for image registration is completed. If not completed (NO in step S05), the process waits for completion in step S25. If the image registration waiting is completed (YES in step S25), the present process is terminated, but the front sheet 400 is conveyed to the image transfer unit 220 by driving the registration roller pair 330.

  As described above, in this embodiment, when the trailing edge 401 of the front sheet 400 waiting for conveyance due to the conveyance stop to the image transfer unit 220 by the registration roller pair 330 exists in the detection range of the manual sheet feed sensor 253. By feeding the next sheet by avoiding the state in which the manual sheet feed sensor 253 cannot detect the leading edge of the next sheet by forming the second loop 420 on the previous sheet 400, the next sheet is fed. Therefore, if the second loop 420 is not formed, even if the trailing edge 401 of the front paper 400 waiting for conveyance is in the detection range of the manual paper feed sensor 253, the subsequent paper is fed. The paper feed can be confirmed early by starting early, and as a result, the start of image formation on the transfer belt 201 can be accelerated and productivity can be improved.

  In the above embodiment, the second loop 420 is formed on the front paper 400 so that the rear end portion 401 of the front paper 400 is retracted from the detection range of the manual paper feed sensor 253.

  However, the method of retracting the rear end portion 401 of the front paper 400 from the detection range of the manual paper feed sensor 253 is not limited to the formation of the second loop 420, and may be, for example, the embodiment shown in FIG. .

  In the embodiment of FIG. 9, the second roller pair 310 that constitutes a part of the lower guide member 501 among the upper guide member 500 and the lower guide member 501 that constitute the horizontal sheet conveyance path 300. And a guide piece 501a between the paper feed roller pair 252 on the downstream side thereof is configured to be able to rotate downward about one end portion on the second roller pair 310 side. Then, as shown in FIG. 5A, the guide piece 501a is always in a horizontal state and constitutes a part of the paper transport path 300. On the other hand, when the front sheet 400 is waiting on the registration roller pair 330 and the trailing end 401 of the sheet 400 is within the detection range of the manual sheet feed sensor 253, as shown in FIG. The second roller pair 310 side of the piece 501a rotates downward clockwise as indicated by an arrow Y, and the sheet conveyance path 300 is opened between the second roller pair 310 and the paper feed roller pair 252.

  As the guide piece 501a rotates, the trailing end 401 of the paper 400 hangs down along the guide piece 501a due to its own weight, and is retracted from the detection range of the manual paper feed sensor 253. Therefore, the next sheet can be fed, and when the next sheet is detected by the manual sheet feeding sensor 253, the sheet feeding is determined.

  Further, the next sheet may be fed by the embodiment shown in FIG.

  In the embodiment shown in FIG. 10, a plurality of manual sheet feed sensors 254 and 255 are provided on the sheet conveyance path 300 between the second roller pair 310 and the sheet feed roller pair 252, and A solenoid 600 is provided as a switching unit capable of switching the transport path between the paper (preceding paper) and the next paper (following paper). In this embodiment, two manual sheet feed sensors 254 and 255 are provided on the upper and lower sides. If the solenoid is facing downward as shown in FIG. 9A, the front sheet 400 fed from the manual feed tray 250 is moved to the detection range of the upper manual feed sensor 254 as shown in FIG. If it is facing upward, the next sheet 700 can be guided to the detection range of the lower manual sheet feed sensor 255 by switching the conveyance path.

  Using this mechanism, when the front paper 400 is waiting on the registration roller pair 330 and the rear end 401 of the front paper 400 is within the detection range of the upper manual paper feed sensor 254, FIG. ), The next sheet 700 is transported to the detection range of the lower manual sheet feed sensor 255. That is, even if the rear end portion 401 of the front sheet 400 is within the detection range of the upper manual sheet feed sensor 254, the next sheet 700 is fed and conveyed to the lower conveyance path. Thus, the lower manual sheet feed sensor 255 is turned on to confirm the feeding of the next sheet 700, whereby the image forming units 211 to 214 can start image formation on the intermediate transfer belt 201.

  The effects of the embodiment of the present invention will be described with reference to FIGS. 11 and 12.

  FIG. 11 is a timing chart in conventional paper conveyance not applying the embodiment of the present invention.

  (T1_1) and (T1_2) indicate the paper interval time between the previous paper and the next paper, and (T2_1), (T2_2), and (T2_3) are generated after the paper feed is confirmed by the manual feed sensor 253. The time when the image is started and the image forming image reaches the image transfer unit 220 is indicated. (T3_1), (T3_2), and (T3_3) indicate the resist waiting time with the image forming image at the front end of the sheet.

  In FIG. 11, the first sheet starts to be fed and reaches the manual feed sensor 253. Image formation is started after the paper supply is confirmed. After the paper passes the manual paper feed sensor 253, the paper reaches the registration sensor 340, the paper skew is corrected by the registration roller pair 330, and the paper waits at the registration roller pair 330 for image registration. After the synchronization with the image forming image on the intermediate transfer belt 201 is completed, the conveyance of the sheet is resumed, and the image forming unit 220 transfers the image forming image onto the sheet. After the fixing process by the fixing roller pair 350, it is transferred to the discharge tray. It is conveyed. The second sheet waits for the start of sheet feeding until the timing at which the rear end of the front sheet passes through the manual sheet feeding sensor 253 and then reaches the manual sheet feeding sensor 253, and the sheet feeding is started. The interval between the first and second sheets is (T1_1), and similarly, the interval between the second and third sheets is (T1_2). Here, the times of (T1_1) and (T1_2) are the same. In FIG. 11, since the trailing edge of the front sheet remains in the detection range of the manual sheet feed sensor 253 while the registration roller pair 330 is waiting for the sheet, feeding of the next sheet is not started, and the sheet interval is widened. ing.

  FIG. 12 shows a timing chart in paper conveyance using this embodiment.

  Similarly to FIG. 11, (T1_1) and (T1_2) indicate the time between the previous sheet and the next sheet, and (T2_1), (T2_2), and (T2_3) indicate that the sheet is fed to the manual feed sensor 253. Indicates the time it takes for the image to reach the image transfer unit 220 after it has been confirmed, and (T3_1), (T3_2), and (T3_3) are the registration waits with the image formed at the leading edge of the paper. Indicates the time.

  In FIG. 12, the first sheet starts to be fed and reaches the manual feed sensor 253. After it is determined that the sheet has been fed, image formation is started. After the paper passes the manual paper feed sensor 253, the paper reaches the registration sensor 340, the paper skew is corrected by the registration roller pair 330, and the paper waits at the registration roller pair 330 for image registration. At this time, if the rear end of the paper remains in the detection range of the manual paper feed sensor 253, the second loop 420 is formed as described above, so that the rear end of the paper is detected from the detection range of the manual paper feed sensor 253. With this, the second sheet starts to be fed, and when the manual sheet feeding sensor 253 is reached, the second sheet starts to be imaged. Accordingly, the interval between the first sheet and the second sheet (T1_1) does not change between FIGS. 11 and 12, but the second sheet and the third sheet interval (T1_2) advance the image formation timing of the second sheet. Therefore, it becomes shorter than the case of FIG. For this reason, it is possible to increase productivity. Note that (T1_1), (T2_1), (T2_2), (T2_3), (T3_1), and (T3_3) do not change between FIG. 11 and FIG.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, the case where the sheet fed from the manual feed tray 250 is retracted from the detection range of the manual sheet feed sensor 253 or the sheet conveyance path is opened by the rotation of the guide member 500 has been described. The same applies to paper fed from the trays 230 and 240.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 100 Control part 101 CPU
102 ROM
103 RAM
140 Image output device 201 Intermediate transfer belt 211 to 214 Image forming unit 220 Transfer unit 221 Transfer roller pair 250 Manual feed tray 252 Manual paper feed roller pair 253, 254, 255 Manual paper feed sensor 300 Conveyance path 310, 311 For second loop formation Roller pair 320 First loop forming roller pair 330 Registration roller pair (timing adjusting means)
400 Front paper (leading paper)
401 Paper rear end 410 First loop 420 Second loop 500 Guide member 600 Solenoid (switching means)

Claims (20)

A pair of paper feed rollers that feed paper from the paper feed section;
Paper detection means for detecting paper fed from the paper feed unit by the paper feed roller pair;
Image imaging means;
A transfer body on which an image is formed by the image forming means;
A transfer unit that transfers an image formed on the transfer body to a sheet fed by the sheet feeding unit in an image transfer unit;
Timing adjusting means for temporarily stopping the conveyance of the paper to the image transfer unit in order to adjust the transfer timing of the image onto the paper by the transfer means;
An image forming apparatus that starts image formation of the next image on the transfer body by the image forming unit after paper supply is confirmed.
When the trailing edge of the preceding sheet waiting for conveyance due to the conveyance stop to the image transfer unit by the timing adjusting unit exists in the detection range of the sheet detecting unit, the sheet detecting unit detects the leading edge of the next succeeding sheet. An image forming apparatus, comprising: a control unit configured to confirm feeding of the succeeding sheet by feeding the succeeding sheet while avoiding a state in which the portion cannot be detected. The timing adjusting means comprises a pair of registration rollers,
A first roller pair for forming a first loop on the paper between the pair of registration rollers is provided on the upstream side of the registration roller pair in the paper conveyance direction, and the paper is provided on the upstream side of the first roller pair. At least one second roller pair for forming a second loop,
The control means forms at least one second loop on the upstream side of the first roller pair by the second roller pair, and sets the trailing edge of the preceding paper waiting for conveyance to the paper detection means. The image forming apparatus according to claim 1, wherein the sheet detection unit avoids a state in which the leading end portion of the succeeding sheet cannot be detected by retreating from the detection range.   A retracting means for retracting the trailing edge of the preceding sheet waiting for transport from the detection range of the sheet detecting means is provided in a sheet transport path in the vicinity of the sheet detecting means, and the control means includes the retracting means The image forming apparatus according to claim 1, wherein the sheet detection unit avoids a state in which the leading end portion of the succeeding sheet cannot be detected by operating the printer.   The torque force of each roller pair is the registration roller pair> first roller pair> second roller pair> feed roller pair, and the force that the second loop tries to return to <torque force of the second roller pair, The image forming apparatus according to claim 2, wherein   5. The image forming apparatus according to claim 2, wherein the first loop and at least one second loop are formed in order from the downstream side in the paper transport direction. Loop amount detecting means for detecting a loop amount of the second loop;
The control means is such that the loop amount of the second loop detected by the loop amount detection means is such that at least the trailing edge of the preceding paper waiting for conveyance passes the detection range of the paper detection means. The image forming apparatus according to claim 2, wherein the second loop is formed so as to have a necessary loop amount. A plurality of second roller pairs are provided on the upstream side of the first roller pair, and a plurality of second loops can be formed between the roller pairs.
The image forming apparatus according to claim 2, wherein the control unit forms one or a plurality of second loops according to a length of a sheet to be conveyed. The distance between each pair of rollers capable of forming the second loop includes different ones,
The image forming apparatus according to claim 7, wherein the control unit selects between a pair of rollers forming the second loop according to a length of a sheet to be conveyed.   The control means forms the second loop only when the rear end portion of the preceding paper waiting for conveyance can retract the detection range of the paper detection means by forming the second loop. The image forming apparatus according to claim 2.   The control means may be configured such that the second loop forms the second loop even when the trailing edge of the preceding paper that is waiting to be conveyed cannot retract the detection range of the paper detection means. The image forming apparatus according to claim 2, wherein the image forming apparatus is formed.   The image forming apparatus according to claim 2, wherein the control unit forms the second loop when the preceding sheet is conveyed to the registration roller pair.   The control means drives the second roller pair on the upstream side to form the second loop with respect to the preceding sheet waiting for conveyance due to the conveyance stop to the image transfer unit by the registration roller pair. The image forming apparatus according to claim 2.   The control means forms the second loop at the start of conveyance of the preceding sheet waiting for conveyance to the image transfer unit due to the conveyance stop to the image transfer unit by the registration roller pair. The image forming apparatus according to any one of?   The control unit forms the second loop by providing a conveyance speed difference between the downstream roller pair and the upstream second roller pair, and forms the second loop with a target loop amount. The image forming apparatus according to claim 11 or 13, wherein a difference in conveyance speed between the downstream roller pair and the upstream second roller pair is eliminated.   The image forming apparatus according to claim 13, wherein the control unit forms the second loop by accelerating the start timing of the upstream second roller pair than the downstream roller pair.   The image forming apparatus according to claim 11, wherein the control unit forms the second loop by stopping the downstream roller pair earlier than the upstream second roller pair.   The image forming apparatus according to claim 3, wherein the retreating unit is a unit that retreats the rear end of the sheet from the sheet conveyance path by opening a sheet conveyance path in the vicinity of the sheet detection unit. A plurality of the paper detection means, and a switching means for switching a paper transport path passing through each paper detection means for each paper detection means,
4. The image forming apparatus according to claim 1, wherein the control unit avoids a state in which the sheet detection unit cannot detect a leading end portion of the succeeding sheet by switching a sheet conveyance path by the switching unit. A pair of paper feed rollers that feed paper from the paper feed section;
Paper detection means for detecting paper fed from the paper feed unit by the paper feed roller pair;
Image imaging means;
A transfer body on which an image is formed by the image forming means;
A transfer unit that transfers an image formed on the transfer body to a sheet fed by the sheet feeding unit in an image transfer unit;
Timing adjusting means for temporarily stopping the conveyance of the paper to the image transfer unit in order to adjust the transfer timing of the image onto the paper by the transfer means;
An image forming apparatus that starts image formation of the next image on the transfer body by the image forming unit after paper supply is confirmed.
When the trailing edge of the preceding sheet waiting for conveyance due to the conveyance stop to the image transfer unit by the timing adjusting unit exists in the detection range of the sheet detecting unit, the sheet detecting unit detects the leading edge of the next succeeding sheet. And a control step for determining the feeding of the succeeding sheet by feeding the succeeding sheet while avoiding a state in which no part can be detected. A pair of paper feed rollers that feed paper from the paper feed section;
Paper detection means for detecting paper fed from the paper feed unit by the paper feed roller pair;
Image imaging means;
A transfer body on which an image is formed by the image forming means;
A transfer unit that transfers an image formed on the transfer body to a sheet fed by the sheet feeding unit in an image transfer unit;
Timing adjusting means for temporarily stopping the conveyance of the paper to the image transfer unit in order to adjust the transfer timing of the image onto the paper by the transfer means;
In the computer of the image forming apparatus that starts image formation of the next image on the transfer body by the image forming unit after paper supply is confirmed,
When the trailing edge of the preceding sheet waiting for conveyance due to the conveyance stop to the image transfer unit by the timing adjusting unit exists in the detection range of the sheet detecting unit, the sheet detecting unit detects the leading edge of the next succeeding sheet. A sheet conveying program for executing a control step for determining the feeding of the succeeding sheet by feeding the succeeding sheet while avoiding a state in which no part can be detected.

Images