JP6969213B2 - Image forming device, paper transport method and paper transport program - Google Patents

Description

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

In an image forming apparatus, it is a general method to increase the system speed in order to improve the productivity, but 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 for improving productivity, a method of shortening the interval between papers to be fed has been proposed.

For example, in Patent Document 1, when the paper is conveyed from the paper feed cassette, the rear end of the preceding paper and the front end of the succeeding paper are partially overlapped and fed, and only the succeeding paper is stopped at a predetermined timing on the way to form the preceding paper. A method of controlling the paper so that the sheet spacing of the paper is slightly increased has been proposed.

Further, in Patent Document 2, the paper length of the paper to be fed is calculated, the paper spacing is calculated based on the calculated paper length, and the paper spacing is followed by the optimum paper feeding timing based on the paper length and the paper spacing. A method of starting paper feeding has been proposed.

All of these are control-related methods that improve productivity without increasing the system speed, but as will be described below, productivity may not be improved even if these methods are used.

Japanese Unexamined Patent Publication No. 2003-176045 Japanese Unexamined Patent Publication No. 11-59954

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 on which a transferred image is imaged is longer than the paper transport path length from the paper feed cassette to the image transfer section. It is necessary to align the tip of the image imaged in the image transfer unit with the tip of the paper, and the timing is determined by the path length and speed of the image / paper. In this case, in order to avoid wasteful consumption of toner in the image forming process, a method of starting image forming on the transfer body after it is confirmed that the paper has been fed may be adopted.

In such an image forming apparatus, the time required to reach the paper image transfer portion is longer for the image on the transfer body than for the paper transport. You have to wait for it to come into place. Further, even in the case of continuous printing on a plurality of sheets, it is necessary to determine the paper feed confirmation for the succeeding paper, but in order to determine the paper feed confirmation, the rear end portion of the preceding paper is the paper. After passing through the detection sensor, the leading edge of the subsequent paper needs to reach the paper detection sensor. In this case, the leading paper is stopped at the resist roller section and is waiting for the leading edge of the image to come to a predetermined position, and the trailing edge of the leading paper remains within the detection range of the paper detection sensor. If so, the succeeding paper cannot be fed until the preceding paper starts to be conveyed to the image transfer unit and the rear end of the paper passes through the detection range of the paper detection sensor. For this reason, it is necessary to delay the paper feed timing for the succeeding paper, and as a result, the confirmation that the succeeding paper has been fed is delayed, and the start of image formation on the transfer material is delayed, resulting in poor productivity. there were.

The present invention has been made in view of such a technical background, and the rear end portion of the preceding paper waiting for transfer is the detection range of the paper detection means due to the stop of transfer to the image transfer unit by the timing adjusting means. An image forming apparatus and paper that can start feeding the subsequent paper at an early stage and confirm the feeding at an early stage, and can accelerate the start of image formation on the transfer material to improve productivity. The subject is to provide a transport method and a paper transport 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 means for detecting paper fed from the paper feed unit by the paper feed roller pair, an image image forming means, and the image creation. The transfer unit that images an image by the image means, the transfer means that transfers the image imaged on the transfer body to the paper fed by the paper feed roller pair at the image transfer unit, and the transfer means. In order to adjust the transfer timing of the image on the paper, the timing adjusting means for temporarily stopping the transfer of the paper to the image transfer unit is provided, and after the paper feeding is confirmed, the image transfer means transfers the paper to the transfer body. In the image forming apparatus that starts image formation of the next image, when the rear end portion of the preceding paper waiting for transfer due to the stop of transfer to the image transfer unit by the timing adjusting means is within the detection range of the paper detection means. Is to feed the succeeding paper by avoiding a state in which the paper detecting means cannot detect the tip of the next succeeding paper while maintaining the paper transport stop by the timing adjusting means. An image forming apparatus comprising a control means for fixing paper.
(2) The timing adjusting means comprises a pair of resist rollers, and a first roller pair for forming a first loop on the paper between the pair of resist rollers and the pair of resist rollers on the upstream side of the pair of resist rollers in the paper transport direction. The control means is provided with at least one second roller pair for forming a second loop on the paper on the upstream side of the first roller pair, and the control means is provided with the first roller pair by the second roller pair. By forming at least one second loop on the upstream side of the pair and retracting the rear end portion of the preceding paper waiting to be conveyed from the detection range of the paper detecting means, the paper detecting means succeeds the paper. The image forming apparatus according to item 1 above, which avoids a state in which the leading edge of paper cannot be detected.
(3) An evacuation means for retracting the rear end portion of the preceding paper waiting for transfer from the detection range of the paper detection means is provided in the paper transfer path in the vicinity of the paper detection means, and the control means is provided with the control means. The image forming apparatus according to item 1 above, which avoids a state in which the paper detecting means cannot detect the tip of the succeeding paper by operating the retracting means.
(4) The torque force of each roller pair is the registration roller pair> the first roller pair> the second roller pair> the paper feed roller pair, and the force that the second loop tries to return to the original <second roller pair. The image forming apparatus according to item 2 above, which is set to torque force.
(5) The image forming apparatus according to item 2 or 4 above, wherein the first loop and at least one second loop are formed in order from the downstream side in the paper transport direction.
(6) The control means includes a loop amount detecting means for detecting the loop amount of the second loop, and the control means is waiting for at least the transfer of the loop amount of the second loop detected by the loop amount detecting means. The second loop is formed so that the rear end portion of the preceding paper has a loop amount required to pass through the detection range of the paper detecting means. Image forming device.
(7) A plurality of second roller pairs are provided on the upstream side of the first roller pair so that a plurality of second loops can be formed between the roller pairs, and the control means is a sheet of paper to be conveyed. The image forming apparatus according to any one of 2, 4 to 6 above, which forms one or a plurality of second loops depending on the length.
(8) The distance between the roller pairs that can form the second loop is different, and the control means has the roller pairs that form the second loop according to the length of the paper to be conveyed. The image forming apparatus according to item 7 above.
(9) The control means has the second loop only when the rear end portion of the preceding paper waiting for transfer can evacuate the detection range of the paper detection means by forming the second loop. The image forming apparatus according to any one of 2, 4 to 8 above.
(10) The control means said that even if the rear end portion of the preceding paper waiting for transfer cannot retract the detection range of the paper detecting means even by forming the second loop. The image forming apparatus according to any one of the preceding items 2, 4 to 9, which forms a loop of 2.
(11) The image forming apparatus according to any one of items 2 and 4 to 10 above, wherein the control means forms the second loop when the preceding paper is conveyed to the resist roller pair.
(12) The control means drives the second roller pair on the upstream side with respect to the preceding paper waiting to be conveyed by stopping the transfer to the image transfer unit by the resist roller pair, thereby causing the second loop. The image forming apparatus according to any one of 2, 4 to 11 in the preceding paragraph.
(13) The control means has the second loop formed at the start of transfer of the preceding paper waiting for transfer to the image transfer section due to the stop of transfer of the resist roller pair to the image transfer section. The image forming apparatus according to any one of 4 to 12.
(14) The control means forms the second loop by providing a transport speed difference between the roller pair on the downstream side and the second roller pair on the upstream side, and the second loop is formed by the target loop amount. 11. The image forming apparatus according to the above item 11 or 13, which eliminates the difference in transport speed between the roller pair on the downstream side and the second roller pair on the upstream side.
(15) The image forming apparatus according to item 13 above, wherein the control means forms the second loop by advancing the start timing of the second roller pair on the upstream side of the roller pair on the downstream side.
(16) The image forming apparatus according to item 11 above, wherein the control means causes the downstream roller pair to stop earlier than the upstream second roller pair to form the second loop.
(17) The image forming apparatus according to item 3 above, wherein the retracting means is a means for retracting the rear end portion of the paper from the paper transport path by opening the paper transport path in the vicinity of the paper detecting means.
(18) A plurality of the paper detecting means are provided, and a switching means for switching a paper transport path passing through the paper detecting means for each paper detecting means is provided, and the control means transports the paper by the switching means. The image forming apparatus according to item 1 or 3 above, which avoids a state in which the paper detecting means cannot detect the tip of the succeeding paper by switching the route.
(19) A paper feed roller pair for feeding paper from the paper feed unit, a paper detection means for detecting paper fed from the paper feed unit by the paper feed roller pair, an image image forming means, and the image creation. The transfer unit that images an image by the image means, the transfer means that transfers the image imaged on the transfer body to the paper fed by the paper feed roller pair at the image transfer unit, and the transfer means. In order to adjust the transfer timing of the image on the paper, the timing adjusting means for temporarily stopping the transfer of the paper to the image transfer unit is provided, and after the paper feeding is confirmed, the image transfer means transfers the paper to the transfer body. When the rear end of the preceding paper waiting to be conveyed by the image forming apparatus for starting the image formation of the next image due to the stop of the transfer to the image transfer unit by the timing adjusting means is within the detection range of the paper detecting means. Is to feed the succeeding paper by avoiding a state in which the paper detecting means cannot detect the tip of the next succeeding paper while maintaining the paper transport stop by the timing adjusting means. A paper transport method characterized by performing a control step to determine the paper.
(20) A paper feed roller pair for feeding paper from the paper feed unit, a paper detection means for detecting the paper fed from the paper feed unit by the paper feed roller pair, an image image forming means, and the image creation. The transfer unit that images an image by the image means, the transfer means that transfers the image imaged on the transfer body to the paper fed by the paper feed roller pair at the image transfer unit, and the transfer means. In order to adjust the transfer timing of the image on the paper, the timing adjusting means for temporarily stopping the transfer of the paper to the image transfer unit is provided, and after the paper feeding is confirmed, the image transfer means transfers the paper to the transfer body. In the computer of the image forming apparatus that starts image formation of the next image, the rear end portion of the preceding paper waiting for transfer due to the stop of transfer to the image transfer unit by the timing adjusting means exists in the detection range of the paper detection means. When this is done, the succeeding paper is fed by avoiding a state in which the paper detecting means cannot detect the tip of the next succeeding paper while maintaining the paper transport stop by the timing adjusting means. A paper transport program for executing control steps to confirm the paper feed.

According to the invention described in the preceding paragraph (1), when the rear end portion of the preceding paper waiting for transfer due to the stop transfer to the image transfer unit by the timing adjusting means equivalent to the resist roller is within the detection range of the paper detection means. Confirms the paper feeding by feeding the succeeding paper while avoiding the state in which the paper detecting means cannot detect the tip of the next succeeding paper while maintaining the paper transport stop by the timing adjusting means. Therefore, even if the rear end of the preceding paper waiting to be conveyed is within the detection range of the paper detecting means, it is possible to start feeding the succeeding paper at an early stage and confirm the feeding at an early stage. As a result, it is possible to accelerate the start of image formation on the transfer material and improve the productivity.

According to the invention described in the preceding paragraph (2), a first roller pair for forming a first paper loop with the resist roller pair is provided on the upstream side of the resist roller pair which is a timing adjusting means. 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 paper on the upstream side of the first roller pair to form a second loop of the preceding paper waiting to be conveyed. Since the rear end portion is retracted from the detection range of the paper detecting means, the state in which the paper detecting means cannot detect the front end portion of the succeeding paper can be reliably avoided by a relatively simple method.

According to the invention described in the preceding paragraph (3), the evacuation means for retracting the rear end portion of the preceding paper waiting for transfer from the detection range of the paper detection means provided in the paper transfer path in the vicinity of the paper detection means. By operating the above, it is possible to reliably avoid a state in which the paper detecting means cannot detect the tip of the succeeding paper.

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

According to the invention described in the preceding paragraph (5), since the first loop and at least one second loop are formed in order from the downstream side in the paper transport direction, the upstream side loop affects the downstream side loop. It is possible to reliably retract the rear end portion of the preceding paper waiting to be conveyed from the detection range of the paper detecting means without exerting the above.

According to the invention described in the preceding paragraph (6), the loop amount of the second loop detected by the loop amount detecting means is such that at least the rear end portion of the preceding paper waiting to be conveyed passes through the detection range of the paper detecting means. Since the second loop is formed so that the amount of loops required for the paper is increased, it is possible to reliably avoid a state in which the paper detecting means cannot detect the tip of the next succeeding paper.

According to the invention described in the preceding paragraph (7), since one or a plurality of second loops can be formed depending on the length of the paper to be conveyed, the rear end portion of the preceding paper waiting to be conveyed is used as the paper. It can be reliably evacuated from the detection range of the detection means.

According to the invention described in the preceding paragraph (8), the distance between the roller pairs capable of forming the second loop is different, and the rollers forming the second loop are formed according to the length of the paper to be conveyed. Since the pair spacing is selected, the second loop can be formed at a position where the load on the paper due to the formation of the second loop is small.

According to the invention described in the preceding paragraph (9), the second loop is formed only when the rear end portion of the preceding paper waiting to be conveyed can evacuate the detection range of the paper detecting means. 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 the preceding paragraph (10), even when the rear end portion of the preceding paper waiting to be conveyed cannot retract the detection range of the paper detecting means even by forming the second loop, the second loop is formed. Since the second loop is formed, by forming the second loop in advance, the rear end of the paper passes through the detection range when the paper waiting to be conveyed is restarted by the drive of the resist roller pair. The time can be shortened and it will contribute to the improvement of efficiency.

According to the invention described in the preceding paragraph (11), since the second loop is formed when the preceding paper is conveyed to the resist roller pair, the second loop can be formed from an early stage, and the image formation is started accordingly. Can be accelerated and productivity can be improved.

According to the invention described in the preceding paragraph (12), the second roller pair on the upstream side is driven with respect to the preceding paper waiting to be conveyed by stopping the transfer to the image transfer unit by the resist roller pair. Since the formation of the second loop can be delayed, 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 resist rollers are not driven, the second loop can be formed accurately.

According to the invention described in the preceding paragraph (13), a second loop is formed at the start of transfer of the preceding paper waiting for transfer to the image transfer section due to the stop of transfer to the image transfer section by the resist roller pair. 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 paragraph (14), a second loop is formed by providing a transport speed difference between the roller pair on the downstream side and the second roller pair on the upstream side, and the target loop amount is the first. After forming the second loop, the transfer speed difference between the roller pair on the downstream side and the second roller pair on the upstream side is eliminated, so that the second loop can be reliably formed.

According to the invention described in the preceding paragraph (15), the second loop can be reliably formed by advancing the start timing of the second roller pair on the upstream side with respect to the roller pair on the downstream side.

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

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

According to the invention described in the preceding paragraph (18), by switching the paper transport path, it is possible to avoid a state in which the paper detecting means cannot detect the tip of the succeeding paper.

According to the invention described in the preceding paragraph (19), even if the rear end of the preceding paper waiting to be conveyed is within the detection range of the paper detecting means, feeding of the succeeding paper is started early and fed. Paper can be fixed at an early stage, and the start of image formation on the transfer body can be accelerated to improve productivity.

According to the invention described in the preceding paragraph (20), even if the rear end of the preceding paper waiting to be conveyed is within the detection range of the paper detecting means, feeding of the succeeding paper is started early and fed. It is possible to make the computer of the image forming apparatus execute a process that can perform paper determination at an early stage and, by extension, accelerate the start of image formation on the transfer body and improve the productivity.

It is a figure which shows the schematic structure of the paper transport path in the image forming apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the electric structure of an image forming apparatus. It is a schematic block diagram of the transport path of the paper to be fed from a manual feed tray. It is a flowchart which shows the conventional paper transfer control process from the feeding of the paper 400 from the manual feed tray 250 to the feeding to the resist roller pair 330. It is a flowchart which shows the conventional paper transport process at the time of continuous printing on a plurality of sheets. It is a figure for demonstrating the state in which the rear end portion of the front paper is retracted from the detection range of the manual paper feed sensor by forming the second loop in the front paper. It is a figure for demonstrating the state in which a plurality of 2nd loops can be formed. It is a flowchart which shows the transfer process when the rear end part of the front paper is retracted from the detection range of the manual paper feed sensor. (A) and (B) are diagrams for explaining other embodiments of the present invention. (A) and (B) are diagrams for explaining other further embodiments of the present invention. It is a timing chart in the conventional paper transport. It is a timing chart in the paper transport which concerns on this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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

In FIG. 1, reference numeral 201 is an endless intermediate transfer belt as a transfer body, and the intermediate transfer belt 201 is driven and conveyed in a certain direction by a driving roller 201a and a driven roller 201b.

4 having photoconductor drums 211a to 214a for forming toner images of each color of Y (yellow), M (magenta), C (cyan), and K (black) along the transport path of the intermediate transfer belt 201. The image forming units 211 to 214 are arranged in order. Then, the image imaged by each image forming unit 211 to 214 and transferred onto the intermediate transfer belt 201 is passed through the secondary transfer roller pair 221 arranged in the image transfer unit 220, whereby the secondary transfer roller is also used. It is designed to be transferred to the paper by superimposing it on the paper passing through the pair 221.

Further, the upper and lower paper feed cassettes 230 and 240 are provided, and the paper accommodated in the upper paper feed cassette 230 is taken out from the paper feed cassette 230 by the pickup roller 231 and vertically 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 accommodated in the lower paper feed cassette 240 is also 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 fed to the vertical transport path. The paper is fed to the horizontally arranged paper transport path 300 by the second-stage vertical transport roller pair 243 provided in the paper transport path 300. The first-stage paper feed sensor 234 and the second-stage paper feed sensor 234 for detecting the paper fed from the paper feed cassettes 230 and 240 are on the output side of each of the paper feed rollers 232 and 242 of the upper and lower paper feed cassettes 230 and 240. Each of the paper feed sensors 244 is provided.

Further, in this embodiment, the manual feed tray 250 is provided so that the paper set in the manual feed tray 250 is taken in by the pickup roller 251 and fed and conveyed to the paper transport path 300 by the paper feed roller pair 252. It has become. A manual feed sensor 253 for detecting the paper fed from the manual feed tray 250 is provided on the output side of the paper feed roller pair 252 of the manual feed cassette 250.

Further, a second loop forming roller pair 310 is arranged on the paper transport path 300 continuing from the manual feed tray 250, and a first loop forming roller pair 320 is arranged on the downstream side of the second loop forming roller pair 310. Is arranged, and the paper fed and conveyed from the upper paper feed cassette 230 and the lower paper feed cassette 240 is conveyed between the first loop forming roller pair 320 and the second loop forming roller pair 310. It is designed to join the route 300.

A resist roller pair 330 is arranged between the first loop forming roller pair 320 and the image transfer unit 220 in the paper transport path 300, and the resist roller pair 330 is located upstream of the resist roller pair 330. A resist sensor 340 that detects the conveyed paper is arranged.

The resist roller pair 330 is based on the paper detection result of the resist sensor 340 in order to adjust the timing of transferring the image imaged on the intermediate transfer belt 201 to the paper by the secondary transfer roller pair 221 in the image transfer unit 220. It serves to temporarily stop the transfer of the paper to the image transfer unit 220. Further, the first loop forming roller pair 320 forms a first loop on the paper between the resist roller pair 330 and the first loop forming roller pair 320, and the second loop forming roller pair 310 manually feeds the paper. With respect to the paper fed from the tray 250, a second loop is formed on the paper between the first loop forming roller pair 320 and the second loop forming roller pair 310. Will be described later.

The paper 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 paper ejection tray (not shown) by the paper ejection roller pair 360. A paper ejection sensor 370 for detecting the paper to be ejected is provided on the upstream side of the paper ejection roller pair 360.

FIG. 2 is a block diagram showing an electrical configuration of an 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, and wireless. It is equipped with a communication interface (wireless communication I / F) 170, an authentication unit 180, and the like, and is 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 comprehensively controls the entire image forming apparatus 1 by executing an operation program stored in the ROM 102 or the like. For example, the copy function, the printer function, the scan function, the facsimile function, and the like are controlled to be executable. In particular, in this embodiment, paper transport control and the like are performed when forming an image on paper executed by an image output device at the time of copying or printing, and the details will be described later.

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

The S-RAM 103 is a work area when the CPU 101 executes a program, and temporarily stores the 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 the time and functions as an internal timer to measure the processing time and the like.

The fixed storage device 110 is composed of 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 image pickup unit, reads a document set on a platen glass by scanning the document, and converts the image of the scanned document into image data which is an electric signal.

The operation panel 130 is used when the user gives an instruction such as a job to the image forming apparatus 1 and makes various settings, 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 to reset the settings, 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. Is.

The display unit 134 is composed of, for example, a liquid crystal display device and displays a message, 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 a copy image generated from image data of a document read by the image reader 120 and print data transmitted from an external terminal device or the like on paper and outputs it as a printed matter. ..

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

The network I / F 160 functions as a communication means for transmitting / receiving 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 the authentication information of the user who logs in, compares and collates this authentication information with the collation information stored in the fixed storage device 110 or the like in advance, and performs authentication. It should be noted that the comparison and collation between the user's authentication information and the collation information may be performed by an external authentication server, and the authentication may be performed by the authentication unit 180 receiving the authentication result from the authentication server.

FIG. 3 is a schematic configuration diagram of a transport path for paper fed from the manual feed tray 250, and shows the configuration from the manual paper feed roller pair 252 to the resist roller pair 330 among the configurations shown in FIG. 1. , The resist sensor 340 is omitted.

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

The paper 400 that has passed through the manual 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 resist roller pair 330. Then, for the paper resist that aligns the head of the image image with the head of the paper 400, the rotational drive of the resist roller pair 330 is stopped to stop the paper 400 and put it on standby. Further, in order to correct the skew of the paper 400, the first loop 410 is formed on the paper 400 between the resist roller pair 330 and the first loop forming roller pair 320 by the first loop forming roller pair 320. .. When the synchronization timing by the paper resist arrives, the resist roller pair 330 is driven to start transporting the waiting paper 400 to the image transfer unit 220 formed in the nip portion of the secondary transfer roller pair 221. Paper is ejected through a well-known image transfer process.

FIG. 4 is a flowchart showing a conventional paper transport control process from feeding paper 400 from the manual feed tray 250 to feeding the paper 400 to the resist roller pair 330 as described above. The processing shown in the flowcharts shown in FIGS. 4 and 5 and later is executed by operating the CPU 101 of the image forming apparatus 1 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 feeding, the manual paper feeding sensor 253 detects the paper 400 and turns it on, and the paper feeding is confirmed. When the paper feed is confirmed, the image forming units 211 to 214 start image formation on the intermediate transfer belt 201. In step S02, the fed paper 400 is conveyed to the resist roller pair 330. In step S03, the drive of the resist roller pair 330 is stopped to wait for the paper 400 (waiting for image registration), and the paper is placed between the resist roller pair 330 and the first loop forming roller pair 320 for skew correction. Let 400 form the first loop 410.

Next, in step S04, it is determined whether or not the image resist waiting is completed, and if it is not completed (NO in step S04), the process waits in step S04 and waits until the completion. If the waiting for the image resist is completed (YES in step S04), this process is terminated, but the paper 400 is conveyed to the image transfer unit 220 by the drive of the resist roller pair 330.

The flowchart of FIG. 5 shows a conventional paper transport process in the case of continuous printing on a plurality of sheets of paper.

In step S11, it is checked whether or not there is a front sheet (preceding sheet) 400, and if not (NO in step S11), the process proceeds to step S13. If there is a front paper 400 (YES in step S11), in step S12, whether the front paper 400 has the manual paper feed sensor 253 turned on, in other words, the rear end of the front paper 400 is the manual paper feed sensor 253. Check if it is 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. 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 moved to the image transfer unit 220. Since it has been transported, the process proceeds to step S13.

In step S13, the next paper (subsequent paper) is fed from the bypass tray 250. By this paper feeding, the manual paper feeding sensor 253 is turned on by the succeeding paper, and the paper feeding is confirmed. When the paper feed is confirmed, the image forming units 211 to 214 start image formation on the intermediate transfer belt 201. In step S14, the fed paper is conveyed to the resist roller pair 330. In step S15, the drive of the resist roller pair 330 is stopped to wait for the paper (waiting for image registration), and the paper is put on the paper between the resist roller pair 330 and the first loop forming roller pair 320 for skew correction. Form the first loop.

Next, in step S16, it is determined whether or not the image resist waiting is completed, and if it is not completed (NO in step S16), the process waits in step S04 and waits until the completion. If the waiting for the image resist is completed (YES in step S16), this process is terminated, but the paper is conveyed to the image transfer unit 220 by the drive of the resist roller pair 330.

In the process shown in the flowchart of FIG. 5, the front paper 400 turns off the manual paper feed sensor 253, that is, the rear end portion 401 of the front paper 400 waits for the manual paper feed sensor 253 to pass, and the succeeding paper is fed. However, even if the front paper 400 does not wait for the manual paper feed sensor 253 to be turned off, the succeeding paper reaches the manual paper feed sensor 253 after the rear end 401 of the front paper 400 has passed through the manual paper feed sensor 253. Subsequent paper may be started to be fed at such a timing.

However, if the front paper (preceding paper) 400 continues to stand by at the registration roller pair 330 with the manual feed sensor 253 turned on at the rear end 401, the succeeding paper cannot be fed and the succeeding paper cannot be fed. Does not turn on the manual paper feed sensor 253, so that the subsequent paper feed is not confirmed. Therefore, as in the present embodiment, when the image transfer path length of the intermediate transfer belt 201 on which the transfer image is imaged is longer than the paper transport path length from the manual feed tray 250 to the image transfer unit 220, the subsequent image transfer path length is longer. Although the image formation of the paper can be started, the image feeding is not confirmed because the paper feed is not confirmed, which reduces the productivity.

Therefore, in this embodiment, as shown in FIG. 6, the front paper 400 is formed with the second loop 420 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 pulled out from the manual paper feed sensor 253, and the manual paper feed sensor 253 is forcibly turned off. And controls to enable the start of paper feed for subsequent paper. When the paper feed of the succeeding paper is started and the manual paper feed sensor 253 is turned on, the paper feed of the succeeding paper is confirmed, so that the paper is transferred to the succeeding paper even if the front paper 400 is waiting on the resist roller pair 330. Image formation is started, and the start of image formation can be accelerated by that amount, improving productivity.

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

Further, as shown in FIG. 7, by arranging a plurality of second roller pairs 311 and 312 at intervals on the upstream side of the first roller pair 320, it is possible to form a plurality of second loops 420. However, one or a plurality of second loops 420 may be formed depending on the length of the front paper 400 to be conveyed. For example, in the case of long paper, if the rear end portion 401 of the paper 400 cannot be retracted from the detection range of the manual paper feed sensor 253 by forming only one second loop 420, as shown in FIG. Two or more second loops 420 may be formed. Further, the distance between the first roller pair 320 and the second roller pair 311 closest to the upstream side and the distance between each second roller pair 311 and 312 are set to different intervals according to the length of the front paper 400. Then, the roller pairs forming the second loop 420 may be selected.

Here, the first loop 410 for cue correction formed on the front paper 400 between the resist 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. Each loop of the second loop 420 formed between the second loop 420 and the second loop 420 formed between the second roller pair 311 and 312 on the upstream side thereof is downstream in the paper transport direction. Formed in order from the first loop 410 on the side, the loop on the upstream side does not affect the loop on the downstream side, and the rear end portion 401 of the front paper 400 waiting to be conveyed is manually fed by the paper feed sensor 253. It is desirable because it can be reliably retracted from the detection range.

Further, the torque force of each roller pair is set to resist roller pair 330> first roller pair 320> second roller pair 310> paper feed roller pair 252, so that the paper 400 is properly conveyed by each roller pair. It is desirable in that it can be done. Further, the force that the second loop 420 tries to return to the original position <the torque force of the second roller pair 310, 311 and 312 is set, while the front paper 400 is properly conveyed by each roller pair. It 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 paper 400 is waiting for the image resist on the resist roller pair 330, or when the paper 400 is being conveyed to or rushed into the resist roller pair 330. It may be the time when the transfer of the front sheet 400, which is waiting to be transferred by the resist roller pair 330, to the image transfer unit 220 is started.

When the second loop 420 is formed when the front paper 400 is conveyed to the resist roller pair 330, the second loop 420 can be formed from an early stage, and the start of image formation can be accelerated by that amount, thereby increasing productivity. Can be improved. In this case, a second loop 420 is formed by providing a transport speed difference between the downstream roller pair 320, 311 and the upstream second roller pair 310, 311 and 312, and the target loop amount is used. After forming the second loop 420, the transfer speed difference between the downstream roller pair 320, 311 and the upstream second roller pair 310, 311 and 312 may be eliminated. Alternatively, the second loop 420 may be formed by stopping the downstream roller pair 320 and 311 earlier than the upstream second roller pair 310, 311 and 312.

Further, when the second loop 420 is formed with respect to the front paper 400 waiting to be conveyed by stopping the transfer to the image transfer unit 220 by the resist roller pair 330, the formation of the second loop 420 can be delayed. , The load on the front paper 400 due to the formation of the second loop 420 can be reduced. Moreover, since the resist 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 second roller pair 310, 311 and 312 on the upstream side with respect to the front paper 400 waiting to be conveyed by the resist roller pair 330.

Further, when the second loop 420 is formed at the start of the transfer of the front paper 400 waiting to be transferred to the image transfer unit 220 due to the stop of transfer to the image transfer unit 220 by the resist roller pair 330, the second loop 420 is formed. The formation of the second loop 420 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 advancing the start timing of the second roller pair 310, 311 and 312 on the upstream side of the roller pair on the downstream side.

Further, only when the rear end portion 401 of the front paper 400 waiting to be conveyed can retract the detection range of the manual paper feed sensor 253 by forming the second loop 420, the second loop 420 is formed. Is also good. If the rear end portion 401 of the front paper 400 waiting to be conveyed cannot retract the detection range of the manual paper feed sensor 253 due to the formation of the second loop 420, the second loop 420 is not formed, so that the second loop 420 is not formed. The formation of the loop 420 can prevent an unnecessary load from being applied to the paper 400.

On the other hand, even if the rear end portion 401 of the front paper 400 waiting to be conveyed cannot retract the detection range of the manual paper feed sensor 253 due to the formation of the second loop 420, the front paper 400 is second. Loop 420 may be formed. In this case, by forming the second loop 420 in advance, the rear end portion 401 of the paper passes through the detection range when the front paper 400 waiting to be conveyed is restarted by the drive of the resist roller pair 330. It can shorten the time to do it and contribute to the improvement of efficiency.

FIG. 8 is a flowchart showing a transfer process when the rear end portion 401 of the front paper 400 is retracted from the detection range of the manual paper feed sensor 253.

In step S21, paper is fed from the manual feed tray 250. By this paper feeding, the manual paper feeding sensor 253 detects the paper 400 and turns it on, and the paper feeding is confirmed. When the paper feed is confirmed, the image forming units 211 to 214 start image formation on the intermediate transfer belt 201. In step S22, the fed paper 400 is conveyed to the resist roller pair 330. In step S23, the drive of the resist roller pair 330 is stopped to wait for the paper 400 (waiting for image registration), and the paper is placed between the resist roller pair 330 and the first loop forming roller pair 320 for skew correction. Let 400 form the first loop 410.

Next, in step S24, it is checked whether or not there is a next sheet (subsequent sheet), and if not (NO in step S24), the process proceeds to step S25. If there is a next sheet (YES in step S24), in step S26, it is checked whether or not the own sheet (previous sheet) has the manual feed sensor 253 turned on. If it is not turned on (NO in step S26), the process proceeds to step S25. If it is turned on (YES in step S26), in step S27, a second loop 420 is formed to retract the paper rear end portion 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 portion 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 paper feed of the next paper is confirmed, and the image formation on the intermediate transfer belt 201 by the image formation units 211 to 214 is started.

In step S25, it is determined whether or not the image resist waiting is completed, and if it is not completed (NO in step S05), the process waits in step S25 and waits until the completion. If the waiting for the image resist is completed (YES in step S25), this process is terminated, but the front sheet 400 is conveyed to the image transfer unit 220 by the drive of the resist roller pair 330.

As described above, in this embodiment, when the rear end portion 401 of the front paper 400 waiting for transfer due to the stop of transfer to the image transfer unit 220 by the resist roller pair 330 is within the detection range of the manual paper feed sensor 253. By forming a second loop 420 on the front paper 400 to avoid the situation where the manual paper feed sensor 253 cannot detect the tip of the next paper, the next paper is fed by feeding the next paper. Since it is confirmed, if the second loop 420 is not formed, even if the rear end portion 401 of the front paper 400 waiting to be conveyed is within the detection range of the manual paper feed sensor 253, the subsequent paper is fed. It is possible to start early and confirm the paper feed at an early stage, and by extension, it is possible to accelerate the start of image formation on the transfer belt 201 and improve the productivity.

In the above embodiment, by forming the second loop 420 on the front paper 400, 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, which constitutes a part of the lower guide member 501 among the upper guide member 500 and the lower guide member 501 constituting the horizontal paper transport path 300. The guide piece 501a between the paper feed roller pair 252 on the downstream side thereof is configured to be rotatable downward about one end portion on the second roller pair 310 side. Then, as shown in FIG. 3A at all times, the guide piece 501a is in a horizontal state and constitutes a part of the paper transport path 300. On the other hand, when the front paper 400 is on standby at the resist roller pair 330 and the rear end portion 401 of the paper 400 is within the detection range of the manual paper feed sensor 253, the guide is as shown in FIG. The second roller pair 310 side of the piece 501a rotates downward clockwise as indicated by the arrow Y, and opens the paper transport path 300 between the second roller pair 310 and the paper feed roller pair 252.

As the guide piece 501a rotates, the rear end portion 401 of the paper 400 hangs downward along the guide piece 501a due to the weight of the paper 400, and is retracted from the detection range of the manual feed sensor 253. Therefore, the next paper can be fed, and when the next paper is detected by the manual feed sensor 253, the paper feed is confirmed.

Further, according to the embodiment as shown in FIG. 10, the next paper may be fed.

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

Using this mechanism, when the front paper 400 is on standby at the resist roller pair 330 and the rear end portion 401 of the front paper 400 is within the detection range of the upper manual paper feed sensor 254, the figure (B). ), The solenoid is switched upward to convey the next paper 700 to the detection range of the lower manual feed sensor 255. That is, even if the rear end portion 401 of the front paper 400 is within the detection range of the upper manual feed sensor 254, the next paper 700 is fed and conveyed to the lower transfer path to convey the next paper 700. The lower manual paper feed sensor 255 is turned on to confirm the paper feed of the next paper 700, whereby image formation on the intermediate transfer belt 201 by the image formation units 211 to 214 can be started.

11 and 12 show the effect of the embodiment of the present invention.

FIG. 11 is a timing chart in conventional paper transport to which the embodiment of the present invention is not applied.

(T1_1) and (T1_2) indicate the time between the previous paper and the next paper, and (T2_1), (T2_2) and (T2_3) are created after the paper feed is confirmed by the manual feed sensor 253. The time when the image is started and the image transfer reaches the image transfer unit 220 is shown, and (T3_1), (T3_2), and (T3_3) indicate the time waiting for registration with the image image at the tip of the paper.

In FIG. 11, the first sheet of paper is started to be fed and reaches the manual feed sensor 253. After the paper feed is confirmed, image drawing is started. After the paper passes through the manual feed sensor 253, it reaches the resist sensor 340, the paper skew is corrected by the resist roller pair 330, and the paper stands by at the resist roller pair 330 for image registration. After the synchronization with the image on the intermediate transfer belt 201 is completed, the transfer of the paper is resumed, the image is transferred to the paper by the image transfer unit 220, and the image is transferred to the discharge tray through the fixing process by the fixing roller pair 350. Is transported. After the rear end of the front paper passes through the manual feed sensor 253, the second sheet waits for the start of paper feed until the timing reaches the manual paper feed sensor 253, and the paper feed is started. The paper spacing between the first and second sheets is (T1_1), and the paper spacing 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 rear end of the front paper remains in the detection range of the manual paper feed sensor 253 while the paper is waiting on the resist roller pair 330, the next paper is not started to be fed and the paper spacing is widened. ing.

FIG. 12 shows a timing chart in paper transport using the present embodiment.

Similar to FIG. 11, (T1_1) and (T1_2) indicate the time between the sheets of the previous sheet and the next sheet, and (T2_1), (T2_2) and (T2_3) indicate that the paper is fed to the manual paper feed sensor 253. The time until the image is reached at the image transfer unit 220 after the image is confirmed is shown, and (T3_1), (T3_2), and (T3_3) are waiting for registration with the image at the tip of the paper. Indicates the time of.

In FIG. 12, the first sheet of paper is started to be fed and reaches the manual feed feed sensor 253. After it is confirmed that the paper has been fed, image drawing starts. After the paper passes through the manual feed sensor 253, it reaches the resist sensor 340, the paper skew is corrected by the resist roller pair 330, and the paper stands by at the resist 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 rear end of the paper is removed from the detection range of the manual paper feed sensor 253 by forming the second loop 420 as described above. As a result, the second sheet is started to be fed, and when the manual paper feed sensor 253 is reached, the second image is started to be drawn. As a result, the spacing between the first and second sheets (T1_1) does not change in FIGS. 11 and 12, but the spacing between the second and third sheets (T1_2) advances the image formation timing of the second sheet. Therefore, it is shorter than the case of FIG. Therefore, it is possible to increase productivity. Note that (T1_1), (T2_1), (T2_2), (T2_3), (T3_1), and (T3_3) are the same in FIGS. 11 and 12.

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 paper fed from the manual feed tray 250 is retracted from the detection range of the manual paper feed sensor 253 and the paper transport path is opened by the rotation of the guide member 500 has been described. The same applies to the paper fed from the trays 230 and 240.

1 Image forming device 100 Control unit 101 CPU
102 ROM
103 RAM
140 Image output device 201 Intermediate transfer belt 211-214 Image drawing unit 220 Transfer unit 221 Transfer roller vs. 250 Manual feed tray 252 Manual paper feed roller pair 253, 254, 255 Manual paper feed sensor 300 Transport path 310, 311 For forming the second loop Roller pair 320 First loop forming roller pair 330 Resist roller pair (timing adjusting means)
400 Front paper (preceding 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,
A paper detecting means for detecting the paper fed from the paper feed unit by the paper feed roller pair, and
Image image means and
A transfer body whose image is imaged by the image image forming means,
A transfer means for transferring an image imaged on the transfer body to the paper fed by the paper feed roller pair at the image transfer unit.
In order to adjust the transfer timing of the image to the paper by the transfer means, the timing adjusting means for temporarily stopping the transfer of the paper to the image transfer unit, and the timing adjusting means.
In an image forming apparatus that starts image formation on the transfer body by the image forming means after the paper feeding is confirmed.
When the rear end portion of the preceding paper waiting for transfer due to the stop of transfer to the image transfer unit by the timing adjusting means is within the detection range of the paper detection means, the stop of transfer of the paper by the timing adjusting means is maintained. characterized in that said sheet sensing means remain is provided with a control means by feeding the succeeding sheet to avoid a situation that can not detect the leading end of the next following sheet, to determine the feed of the subsequent paper Image forming apparatus. The timing adjusting means consists of a pair of resist rollers.
A first roller pair for forming a first loop in the paper with the resist roller pair is provided on the upstream side of the resist roller pair in the paper transport direction, and the paper is provided on the upstream side of the first roller pair. Equipped with at least one second roller pair for forming a second loop in the
The control means forms at least one second loop on the upstream side of the first roller pair by the second roller pair, and the paper detecting means detects the rear end portion of the preceding paper waiting to be conveyed. The image forming apparatus according to claim 1, wherein the paper detecting means avoids a state in which the tip end portion of the succeeding paper cannot be detected by retracting from the detection range of the above. An evacuation means for retracting the rear end portion of the preceding paper waiting for transfer from the detection range of the paper detection means is provided in the paper transfer path in the vicinity of the paper detection means, and the control means is the evacuation means. The image forming apparatus according to claim 1, wherein the paper detecting means avoids a state in which the tip end portion of the succeeding paper cannot be detected by operating the above. The torque force of each roller pair is the registration roller pair> the first roller pair> the second roller pair> the paper feed roller pair, and the force that the second loop tries to return to the original position <the torque force of the second roller pair, The image forming apparatus according to claim 2, which is set in 1. The image forming apparatus according to claim 2 or 4, wherein the first loop and at least one of the second loops are formed in order from the downstream side in the paper transport direction. A loop amount detecting means for detecting the loop amount of the second loop is provided.
In the control means, the loop amount of the second loop detected by the loop amount detecting means is such that at least the rear end portion of the preceding paper waiting to be conveyed passes through the detection range of the paper detecting means. The image forming apparatus according to any one of claims 2, 4 or 5, wherein the second loop is formed so as to obtain a required loop amount. A plurality of second roller pairs are provided on the upstream side of the first roller pair so that a plurality of second loops can be formed between the roller pairs.
The image forming apparatus according to any one of claims 2, 4 to 6, wherein the control means forms one or a plurality of second loops depending on the length of the conveyed paper. The spacing 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 means selects between roller pairs forming a second loop according to the length of the conveyed paper. The control means forms the second loop only when the rear end portion of the preceding paper waiting for transfer can evacuate the detection range of the paper detecting means by forming the second loop. The image forming apparatus according to any one of claims 2, 4 to 8. The control means has the second loop even when the rear end portion of the preceding paper waiting to be conveyed cannot retract the detection range of the paper detection means due to the formation of the second loop. The image forming apparatus according to any one of claims 2, 4 to 9. The image forming apparatus according to any one of claims 2, 4 to 10, wherein the control means forms the second loop when the preceding paper is conveyed to the resist roller pair. The control means forms the second loop by driving the second roller pair on the upstream side with respect to the preceding paper waiting to be conveyed by stopping the transfer to the image transfer unit by the resist roller pair. The image forming apparatus according to any one of claims 2, 4 to 11. 2. The image forming apparatus according to any one of 12 to 12. The control means forms the second loop by providing a transport speed difference between the roller pair on the downstream side and the second roller pair on the upstream side, and forms the second loop with the target loop amount. The image forming apparatus according to claim 11 or 13, wherein the transfer speed difference between the roller pair on the downstream side and the second roller pair on the upstream side is eliminated. The image forming apparatus according to claim 13, wherein the control means forms the second loop by accelerating the start timing of the second roller pair on the upstream side of the roller pair on the downstream side. The image forming apparatus according to claim 11, wherein the control means causes the downstream roller pair to stop earlier than the upstream second roller pair to form the second loop. The image forming apparatus according to claim 3, wherein the retracting means is a means for retracting the rear end portion of the paper from the paper transport path by opening the paper transport path in the vicinity of the paper detecting means. A plurality of the paper detecting means are provided, and a switching means for switching a paper transport path passing through the paper detecting means for each paper detecting means is provided.
The image forming apparatus according to claim 1 or 3, wherein the control means avoids a state in which the paper detecting means cannot detect the tip end portion of the succeeding paper by switching the paper transport path by the switching means. A pair of paper feed rollers that feed paper from the paper feed section,
A paper detecting means for detecting the paper fed from the paper feed unit by the paper feed roller pair, and
Image image means and
A transfer body whose image is imaged by the image image forming means,
A transfer means for transferring an image imaged on the transfer body to the paper fed by the paper feed roller pair at the image transfer unit.
In order to adjust the transfer timing of the image to the paper by the transfer means, the timing adjusting means for temporarily stopping the transfer of the paper to the image transfer unit, and the timing adjusting means.
An image forming apparatus that starts image formation on the transfer body by the image forming means after the paper feeding is confirmed.
When the rear end portion of the preceding paper waiting for transfer due to the stop of transfer to the image transfer unit by the timing adjusting means is within the detection range of the paper detection means, the stop of transfer of the paper by the timing adjusting means is maintained. The feature is that the control step for confirming the feeding of the succeeding paper is executed by feeding the succeeding paper while avoiding the state where the paper detecting means cannot detect the tip of the next succeeding paper. Paper transport method. A pair of paper feed rollers that feed paper from the paper feed section,
A paper detecting means for detecting the paper fed from the paper feed unit by the paper feed roller pair, and
Image image means and
A transfer body whose image is imaged by the image image forming means,
A transfer means for transferring an image imaged on the transfer body to the paper fed by the paper feed roller pair at the image transfer unit.
In order to adjust the transfer timing of the image to the paper by the transfer means, the timing adjusting means for temporarily stopping the transfer of the paper to the image transfer unit, and the timing adjusting means.
To the computer of the image forming apparatus, which starts the image formation of the next image on the transfer body by the image forming means after the paper feeding is confirmed.
When the rear end portion of the preceding paper waiting for transfer due to the stop of transfer to the image transfer unit by the timing adjusting means is within the detection range of the paper detection means, the stop of transfer of the paper by the timing adjusting means is maintained. by feeding the succeeding sheet said sheet detection means while is to avoid a situation that can not detect the leading end of the next following sheet, the sheet transport for executing a control step of determining the feeding of the following sheet program.

Images