JP2018118459A - Image formation apparatus - Google Patents

Abstract

An image forming apparatus capable of suppressing a decrease in productivity is provided. An image forming apparatus includes: a transport unit that performs secondary paper feeding that transports a sheet that has reached a registration position to a printing position; a control unit that controls secondary paper feeding to be started at a target interval; A registration sensor that detects a position upstream of the sheet conveyance direction as a detection position, and the control unit detects the arrival time of the arrival sheet that has reached the detection position, and the trailing edge of the preceding sheet passes the detection position. When the time difference between the passage time and the arrival time exceeds the threshold time, the arrival paper is determined to be a delay paper, and if the arrival paper is determined to be a delay paper, the delay paper after the start of the secondary feeding of the delay paper Is transported at a speed higher than the normal transport speed. [Selection] Figure 4

Description

  The present invention relates to an image forming apparatus that prints an image on a sheet.

  Conventionally, an image forming apparatus that conveys a sheet and prints an image on the sheet being conveyed is known. For example, the image forming apparatus disclosed in Patent Document 1 conveys a sheet along a conveyance path that passes through a paper feeding position, a registration position, and a printing position. At the paper feed position, paper is supplied to the transport path. At the registration position, the skew correction of the paper is performed. At the printing position, the image is printed on the paper.

  A registration roller pair is installed at the registration position. The registration roller pair stops rotating when the paper reaches the registration position, and temporarily stops the progress of the paper that has reached the registration position. At this time, the skew of the paper is corrected. Then, the registration roller pair temporarily stops the progress of the sheet at the registration position, and then starts conveying the sheet (secondary sheet feeding).

JP-A-2006-124142

  In some cases, the arrival timing of the paper from the paper feed position to the registration position may be delayed from a predetermined target timing. When the arrival timing of the paper at the registration position is delayed, there is a disadvantage that the start timing of the secondary paper feeding of the paper is delayed.

  For example, normally, a paper sensor for detecting the paper transport state is provided on the paper transport path from the paper feed position to the registration position. Therefore, based on the output value of the paper sensor, it can be determined whether or not the arrival timing of the paper from the paper feed position to the registration position is delayed. When the paper arrival timing from the paper feeding position to the registration position is delayed, the paper arrival speed to the registration position is increased to prevent the paper arrival timing from reaching the registration position from being delayed. Can do. If such control is performed, when images are continuously printed on a plurality of sheets (when a plurality of sheets are continuously conveyed), secondary feeding is performed at a predetermined target interval (a constant interval). Since paper can be started, productivity is not reduced.

  However, even if the sheet conveyance speed from the sheet feeding position to the registration position is increased, the arrival timing of the sheet at the registration position may be delayed. In this case, the interval between the start timing of the secondary paper feeding of the preceding paper and the start timing of the secondary paper feed of the delayed paper, which are conveyed before the delayed paper whose arrival timing at the registration position is delayed, is the target interval. Therefore, even if the secondary paper feeding of the paper to be transported thereafter is started at the target interval, it takes a long time to discharge the final printed paper (productivity is reduced).

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of suppressing a reduction in productivity.

  In order to achieve the above object, an image forming apparatus of the present invention performs a main conveyance path that passes from a sheet feeding position through a registration position and a printing position, and primary sheet feeding that supplies paper from the sheet feeding position to the main conveyance path. The paper is transported from the paper feed position to the registration position, and when the paper reaches the registration position, the paper that has reached the registration position is temporarily stopped and then the paper that has reached the registration position is transported to the printing position 2. A transport unit that performs the next paper feeding, a printing unit that prints an image on a sheet at a printing position, and controls the transport of the paper by the transport unit and the printing of the image onto the paper by the printing unit, and the transport unit includes a plurality of sheets of paper. When the continuous conveyance is performed, the control unit that controls the conveyance of the sheet by the conveyance unit so that the secondary sheet feeding is started at a predetermined target interval, and the registration position of the main conveyance path The position of the sheet conveyance direction upstream side to the detection position than, and a resist sensor for detecting the presence or absence of paper at the detection position. The control unit detects the arrival time of the arrival paper that has reached the detection position based on the output value of the registration sensor, and the passage of the trailing edge of the preceding paper conveyed before the arrival paper has passed the detection position. When the time difference between the time point and the arrival time exceeds a predetermined threshold time, a determination process is performed to determine that the arrival paper is a delayed paper. The conveyance unit is caused to perform high-speed conveyance for conveying the delayed paper at a first conveyance speed faster than a predetermined normal conveyance speed.

  In the configuration of the present invention, when the arrived paper that has reached the detection position of the registration sensor is a delayed paper, the conveyance unit performs high-speed conveyance for the delayed paper, so the delayed paper from the start of the secondary feeding of the delayed paper. The time until the trailing edge passes the detection position of the registration sensor (the time from the start to the end of the secondary feeding of the delayed paper) is shortened. Thereby, the interval between the time when the secondary paper feeding of the delayed paper is started and the time when the secondary paper feeding of the next paper (the paper to be transported from the registration position to the printing position next to the delay paper) is started is made larger than the target interval. Can also be shortened. As a result, even if the arrival of the sheet at the detection position of the registration sensor is delayed, it is possible to suppress an increase in the time taken until the final printed sheet is discharged (suppressing a decrease in productivity). can do).

  According to the configuration of the present invention, it is possible to suppress a decrease in productivity even when the leading edge of the paper reaches the detection position of the registration sensor is delayed.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a hardware configuration of an image forming apparatus according to an embodiment of the present invention. 6 is a timing chart for explaining sheet conveyance control performed by a control unit of an image forming apparatus according to an embodiment of the present disclosure. 6 is a timing chart for explaining sheet conveyance control performed by a control unit of an image forming apparatus according to an embodiment of the present disclosure. 7 is a flowchart for explaining sheet conveyance control performed by the control unit of the image forming apparatus according to the embodiment of the present disclosure.

  In the following, an embodiment of the present invention will be described taking an inkjet image forming apparatus as an example.

<Configuration of image forming apparatus>
As shown in FIG. 1, the image forming apparatus 100 of the present embodiment includes a conveyance path 10 for conveying the paper P. The conveyance path 10 is classified into a main conveyance path 1A and a duplex printing conveyance path 1B. The main transport path 1A reaches the discharge position P4 from the paper feed position P1 through the registration position P2 and the printing position P3 in this order. The duplex printing conveyance path 1B branches from the main conveyance path 1A at a position DP downstream of the printing position P3 in the sheet conveyance direction, and at a position UP upstream of the registration position P2 (registration detection position RP) in the sheet conveyance direction. Merge into the main transport path 1A. The duplex printing conveyance path 1B is not used when executing single-sided printing for printing an image on only one side of the paper P, but used for executing double-sided printing for printing an image on both sides of the paper P (details will be described later). In FIG. 1, the conveyance path of the paper P is indicated by a broken line, and the conveyance direction of the paper P is indicated by an arrow.

  Further, the image forming apparatus 100 includes a transport unit 20 and a printing unit 30. The transport unit 20 transports the paper P along the transport path 10. The printing unit 30 prints an image on the paper P being transported along the transport path 10.

  The transport unit 20 includes a paper feed roller pair 21 and a paper feed side transport roller pair 22. The paper feed roller pair 21 is installed at the paper feed position P1. The paper feed side transport roller pair 22 is installed between the paper feed position P1 and the registration position P2. The number of paper feed side transport roller pairs 22 may be plural or one.

  The paper feed roller pair 21 pulls out the paper P from the paper cassette CA at the paper feed position P1 and supplies it to the transport path 10. In other words, the paper feed roller pair 21 performs primary paper feed. Further, the paper feed roller pair 21 transports the paper P supplied to the transport path 10 along the transport path 10. The paper feed side transport roller pair 22 transports the paper P along the transport path 10 together with the paper feed roller pair 21. As a result, the paper P is transported from the paper feed position P1 toward the registration position P2.

  Further, the transport unit 20 includes a registration roller pair 23. The registration roller pair 23 is installed at the registration position P2. The registration roller pair 23 conveys the paper P conveyed from the paper feeding position P1 toward the printing position P3. In other words, the registration roller pair 23 performs secondary paper feeding.

  The registration roller pair 23 stops rotating when the paper P reaches the registration position P2. Thereby, the progress of the paper P is temporarily stopped, and the skew of the paper P is corrected at that time (the leading end portion of the paper P is bent). Then, the registration roller pair 23 stops the progress of the paper P until a predetermined skew correction time elapses, and then transports the paper P that has reached the registration position P2 to the printing position P3 (secondary feeding). Paper).

  The transport unit 20 includes a belt unit 24. The belt unit 24 is installed at the printing position P3 and transports the paper P at the printing position P3. The printing of the image on the paper P by the printing unit 30 is performed on the paper P conveyed by the belt unit 24.

  The belt unit 24 includes a conveyance belt 241, a driving roller 242, and a driven roller 243. The conveyor belt 241 is stretched by a driving roller 242 and a driven roller 243, and circulates when the driving roller 242 is driven (rotated). When the conveyance belt 241 circulates and the sheet P is conveyed to the printing position P3 in this state, the sheet P that has reached the printing position P3 is conveyed by the conveyance belt 241.

  Further, the transport unit 20 includes a discharge-side transport roller pair 25. The discharge-side transport roller pair 25 is installed between the printing position P3 and the discharge position P4. For example, the number of discharge-side transport roller pairs 25 is plural.

  The discharge-side transport roller pair 25 transports the paper P (printed paper P) transported from the printing position P3 toward the discharge position P4. A discharge tray ET is installed at the discharge position P4. The discharge-side transport roller pair 25 transports the printed paper P and discharges the printed paper P to the discharge tray ET.

  The transport unit 20 includes a transport roller pair 26 for double-sided printing (including a switchback roller pair 26S). The duplex printing conveyance roller pair 26 is installed in the duplex printing conveyance path 1B. For example, the number of the duplex printing conveyance roller pairs 26 is plural. The duplex printing transport roller pair 26 is a transport roller pair used when performing duplex printing, and transports the paper P along the duplex printing transport path 1B.

  The printing unit 30 is installed at a position facing the belt unit 24 (above the belt unit 24), and prints an image on the paper P being conveyed at the printing position P3. The printing of the image on the paper P by the printing unit 30 is performed on the paper P (paper P on the transport belt 241) transported by the belt unit 24.

  The printing unit 30 includes line heads 3C, 3M, 3Y, and 3K for four colors. The line heads 3C, 3M, 3Y and 3K are arranged in this order from the upstream side to the downstream side in the paper transport direction. The line head 3C accommodates cyan ink. The line head 3M contains magenta ink. The line head 3Y contains yellow ink. The line head 3K contains black ink.

  Each of the line heads 3C, 3M, 3Y and 3K has a plurality of nozzles 31 (see FIG. 2) for ejecting ink. Although not shown, each nozzle 31 is provided with a piezoelectric element. By applying a driving voltage to the piezoelectric element of the nozzle 31, the nozzle 31 corresponding to the piezoelectric element to which the driving voltage is applied is driven (nozzle 31). Ink is ejected from the

  Here, double-sided printing will be described. The duplex printing conveyance path 1B is classified into a first conveyance path 11B and a second conveyance path 12B. The first transport path 11B is connected to the position DP of the main transport path 1A. The second transport path 12B is a transport path for switching back the paper P, and is connected to the position UP of the main transport path 1A.

  When performing single-sided printing, the printing unit 30 prints a surface image on the surface of the paper P. Then, the transport unit 20 transports the single-sided printing paper P on which the front surface image is printed along the main transport path 1A and discharges it as it is to the discharge tray ET.

  On the other hand, at the time of executing double-sided printing, when the printing of the front surface image on the paper P is finished, the carrying unit 20 performs a carrying process for double-sided printing. Specifically, the conveyance unit 20 pulls the single-sided printing paper P into the first conveyance path 11B, and causes the single-sided printing paper P to enter the second conveyance path 12B from the first conveyance path 11B. Then, the transport unit 20 performs a reversing process (a process for switching back the single-sided printing paper P) for reversing the orientation of the front and back surfaces of the single-sided printing paper P. At this time, the switchback roller pair 26S rotates forward until the rear end of the single-sided printing paper P passes through the branch point between the first transport path 11B and the second transport path 12B, and the branch point of the single-sided printing paper P The single-sided printing paper P is switched back by reversely rotating at the timing when the trailing edge passes. Thereafter, the transport unit 20 returns the single-sided printing paper P to the position UP of the main transport path 1A.

  In addition, when the conveyance unit 20 returns the single-sided printing paper P to the main conveyance path 1A, the single-sided printing paper P is conveyed again from the registration position P2 toward the printing position P3. That is, at the time of executing double-sided printing, the paper P passes through the printing position P3 twice. At this time, the orientation of the front and back surfaces of the single-sided printing paper P is reversed (the orientation of the front and back surfaces of the paper P that passes again through the printing position P3 is opposite to that when it passed through the printing position P3 last time. ) Accordingly, the printing of the image by the printing unit 30 is performed on the back surface (unprinted surface) of the single-sided printing paper P. That is, the back image is printed on the back surface of the single-sided printing paper P. Thereafter, the transport unit 20 transports the paper P on which the front and back images are printed on the front and back surfaces of the paper P along the main transport path 1A and discharges the paper P to the discharge tray ET.

  For example, when the number of double-sided printing is a predetermined number (for example, three) or less, the front image is continuously printed on all the sheets P, and then the back image is continuously printed on all the sheets P. Done. When the number of double-sided printed sheets exceeds the predetermined number, the front surface image is continuously printed on the predetermined number of sheets P, and then the back side image is printed on the single-sided printed sheet P and the unprinted sheet P is printed. The surface image is printed alternately. As an example, after the first single-sided printing paper P is conveyed from the registration position P2 to the printing position P3, before the second single-sided printing paper P is conveyed to the registration position P2, the fourth sheet The unprinted paper P is conveyed from the paper feeding position P1 to the registration position P2. Thereafter, the second single-sided printing paper P is conveyed to the registration position P2.

  In addition, the image forming apparatus 100 includes a control unit 40 that controls each unit of the image forming apparatus 100 as illustrated in FIG. 2. The control unit 40 includes a CPU 41, a memory 42, and an ASIC 43. The CPU 41 operates based on a control program and data, and performs processing for controlling each unit of the image forming apparatus 100. The memory 42 stores a control program and data for operating the CPU 41. The ASIC 43 performs specific processing such as image processing.

  The control unit 40 is connected to a conveyance motor that rotates a roller of the conveyance unit 20 in order to control conveyance of the paper P by the conveyance unit 20. For example, the transport motor includes a paper feed motor M1, a registration motor M2, a belt motor M3, a discharge motor M4, a duplex printing motor M5, and a switchback motor M6.

  The paper feed side motor M1 is connected to the paper feed roller pair 21 and the paper feed side transport roller pair 22. The control unit 40 controls driving of the paper feed side motor M1 to appropriately rotate the paper feed roller pair 21 and the paper feed side transport roller pair 22. The pair of paper feed rollers 21 receives a driving force from the paper feed motor M1 via a paper feed side clutch (not shown). The control unit 40 controls on / off of the paper feed side clutch, and switches between connection and release of the paper feed roller pair 21 and the paper feed side motor M1.

  The registration motor M <b> 2 is connected to the registration roller pair 23. The control unit 40 controls the driving of the registration motor M2, and appropriately rotates the registration roller pair 23. The registration roller pair 23 receives a driving force from the registration motor M2 via a registration clutch (not shown). The control unit 40 controls on / off of the registration clutch, and switches between connection and release of the registration roller pair 23 and the registration motor M2.

  The belt motor M3 is connected to the driving roller 242 of the belt unit 24. The control unit 40 controls the driving of the belt motor M3 and appropriately rotates the driving roller 242 of the belt unit 24. That is, the control unit 40 appropriately rotates the conveyor belt 411 of the belt unit 24.

  The discharge-side motor M4 is connected to the discharge-side transport roller pair 25. The control unit 40 controls the driving of the discharge side motor M4 and appropriately rotates the discharge side transport roller pair 25. Further, the discharge-side transport roller pair 25 receives a driving force from the discharge-side motor M3 via a discharge-side clutch (not shown). The control unit 40 controls on / off of the discharge side clutch, and switches between connection and release of the discharge side conveyance roller pair 25 and the discharge side motor M4.

  The number of discharge side motors M4 installed is not particularly limited, and can be changed according to the number of discharge side transport roller pairs 25 installed. As an example, a plurality of discharge side motors M <b> 4 are provided, and each discharge side motor M <b> 4 gives a driving force to one to three discharge side transport roller pairs 25. For example, the connection between the discharge-side transport roller pair 25 connected to a certain discharge-side motor M4 and the discharge-side motor M4 is released, and another discharge-side motor M4 is connected to the discharge-side transport roller pair 25. A possible configuration may be adopted.

  The duplex printing motor M5 is connected to the duplex printing transport roller pair 26 other than the switchback roller pair 26S. The control unit 40 controls driving of the double-sided printing motor M5 to appropriately rotate the double-sided printing transport roller pair 26. The duplex printing transport roller pair 26 receives a driving force from a duplex printing motor M5 via a duplex printing clutch (not shown). The control unit 40 controls on / off of the double-sided printing clutch, and switches between connection and release of the double-sided printing conveyance roller pair 26 and the double-sided printing motor M5.

  The number of installed double-sided printing motors M5 is not particularly limited, and can be changed according to the number of installed duplexing conveyance roller pairs 26. As an example, a plurality of double-sided printing motors M <b> 5 are provided, and each double-sided printing motor M <b> 5 applies a driving force to one to three duplex printing conveyance roller pairs 26. For example, the double-sided printing conveyance roller pair 25 connected to a certain double-sided printing motor M5 is disconnected from the double-sided printing motor M5, and another double-sided printing motor M5 is connected to the double-sided printing conveyance roller pair 26. It is also possible to adopt a configuration capable of connecting the two.

  The switchback motor M6 is connected to the switchback roller 26S. The control unit 40 controls the driving of the switchback motor M6 and appropriately rotates the switchback roller pair 26S. That is, the control unit 40 switches between normal rotation and reverse rotation of the switchback roller pair 26S.

  In addition, the control unit 40 is connected to the sheet sensor for detecting the position of the sheet P (the sheet P being conveyed) existing in the conveyance path 10 in order to control the conveyance of the sheet P by the conveyance unit 20. For example, the conveyance path 10 is provided with a plurality of detection positions, and one sheet sensor PS is disposed at each of the plurality of detection positions (a plurality of sheet sensors PS are disposed in the conveyance path 10). The plurality of paper sensors PS change the output value according to the presence or absence of the paper P at the corresponding detection position. Based on the output values of the plurality of paper sensors PS, the control unit 40 detects the presence or absence of the paper P at each detection position (arrival at the leading edge of the paper P and passing through the trailing edge of the paper P). Further, the control unit 40 recognizes the current position of the paper P being conveyed based on the output values of the plurality of paper sensors PS.

  Among the plurality of paper sensors PS, the predetermined paper sensor PS is a registration sensor having a detection position at a position between the paper feed position P1 and the registration position P2 and in the vicinity of the registration position P2. Hereinafter, the registration sensor will be denoted by reference numeral RS, and the detection position of the registration sensor will be denoted by reference numeral RP.

  The control unit 40 is connected to the driver 32 of the printing unit 30 and controls the printing operation of the printing unit 30. The driver 32 is a circuit for controlling the ejection of ink from the nozzles 31 and is provided for each of the line heads 3C, 3M, 3Y, and 3K. Then, the control unit 40 gives an operation instruction to each driver 32 of the line heads 3C, 3M, 3Y, and 3K.

  Note that the drive frequency of the printing unit 30 (ink head) is determined in advance, and the paper transport speed (normal transport speed) is set based on the drive frequency. Then, when there is no conveyance delay in the paper P, the control unit 40 causes the conveyance unit 20 to convey the paper P at the normal conveyance speed.

  In addition, the image forming apparatus 100 includes a communication unit 50. The communication unit 50 is an interface for connecting the image forming apparatus 100 to a network NT such as a LAN. A user terminal 200 (for example, the user terminal 200 is a personal computer, a smartphone, a tablet terminal, or the like) used by a user of the image forming apparatus 100 is connected to the network NT. Then, the control unit 40 accesses the network NT via the communication unit 50 and transmits / receives data to / from the user terminal 200.

  For example, a print request to the image forming apparatus 100 is transmitted from the user terminal 200 (the communication unit 50 receives the print request). The print request from the user terminal 200 includes condition data indicating print execution conditions, image data of an image to be printed, and the like. When the communication unit 50 receives the print request, the control unit 40 causes the conveyance unit 20 to convey the paper P, and causes the printing unit 30 to print an image on the paper P based on the image data included in the print request. Let it be done.

<Paper transport control>
The controller 40 detects the arrival of the leading edge of the paper P at a detection position RP (hereinafter referred to as a registration detection position RP) based on the output value of the registration sensor RS. Then, for example, when a predetermined time has elapsed from the time when the leading edge of the preceding paper P currently being conveyed reaches the registration detection position RP, the control unit 40 performs the next paper P (next to the preceding paper P) to the main conveyance path 1A. Then, the conveyance unit 20 is started to supply the paper P) to be conveyed from the registration position P2 to the printing position P3. Alternatively, the control unit 40 determines the main conveyance path based on the elapsed time from the time when the leading edge of the preceding sheet P or the trailing edge passage is detected at any detection position of the plurality of sheet sensors PS installed in the conveyance path 10. The supply start timing of the next paper P to 1A is measured.

  Furthermore, the control unit 40 starts conveying the sheet P from the registration position P2 to the printing position P3 by the registration roller pair 23 based on the time point when the leading edge of the sheet P reaches the registration detection position RP (secondary paper feeding). Start timing). Specifically, the control unit 40 detects the arrival of the leading edge of the paper P at the registration detection position RP based on the output value of the registration sensor RS, and then the conveyance time of the paper P from the registration detection position RP to the registration position P2. At the timing when the skew correction time is added (referred to as registration time in the following description), the conveyance (secondary paper feeding) of the paper P from the registration position P2 to the printing position P3 by the registration roller pair 23 is performed. Let it begin.

  Here, when a plurality of sheets of paper P are continuously conveyed (when images are continuously printed on a plurality of sheets of paper P), the control unit 40 determines secondary paper feeding by the registration roller pair 23 in advance. The conveyance of the paper P by the conveyance unit 20 is controlled so as to start at the target interval. That is, the control unit 40 starts the secondary paper feeding of the preceding paper P and the secondary paper feeding of the succeeding paper P (the paper to be transported from the registration position P2 to the printing position P3 next to the preceding paper P). The conveyance unit 20 is controlled so that the interval from the time point becomes the target interval. Thereby, ideally, the secondary sheet feeding is started at a constant interval (target interval).

  For example, it is assumed that the first paper P, the second paper P, and the third paper P are conveyed to the registration position P2 in this order. In this case, as shown in FIG. 3, the control unit 40 detects the arrival time point TA1 when the leading edge of the first sheet P reaches the registration detection position RP. Then, when the registration time has elapsed from the arrival time point TA1 (time point TB1), the control unit 40 starts secondary paper feeding of the first paper P. Thereafter, the control unit 40 detects the passage time TC1 when the trailing edge of the first sheet P has passed the registration detection position RP.

  In addition, the control unit 40 sets the second sheet so that the leading edge of the second sheet P reaches the registration detection position RP before the elapsed time T from the passage time TC1 of the first sheet P exceeds a predetermined threshold time Th. While controlling the conveyance of P, the arrival time TA2 at which the leading edge of the second sheet P reaches the registration detection position RP is detected. Then, when the registration time has elapsed from the arrival time TA2 of the second paper P (time TB2), the control unit 40 starts secondary paper feeding of the second paper P. Thereafter, the control unit 40 detects a passing time point TC2 when the trailing edge of the second sheet P passes the registration detection position RP.

  Further, the control unit 40 conveys the third sheet P so that the leading edge of the third sheet P reaches the registration detection position RP before the elapsed time T from the passage time TC2 of the second sheet P exceeds the threshold time Th. In addition to the control, the arrival time TA3 when the leading edge of the third sheet P reaches the registration detection position RP is detected. Then, when the registration time has elapsed from the arrival time TA3 of the third paper P (time TB3), the control unit 40 starts the secondary paper feeding of the third paper P. Thereafter, the control unit 40 detects the passage time TC3 when the trailing edge of the third sheet P passes the registration detection position RP.

  If there is no conveyance delay in the first sheet P to the third sheet P, the secondary sheet feeding can be started at a constant interval (target interval) (see the upper diagram in FIG. 3). However, for example, when a conveyance delay occurs in the second paper P, the arrival time TA2 when the leading edge of the second paper P reaches the registration detection position RP is delayed (see the lower diagram in FIG. 3).

  When the leading edge of the second sheet P reaches the registration detection position RP is delayed, that is, when the time difference T between the passage time TC1 of the first sheet P and the arrival point TA2 of the second sheet P exceeds the threshold time Th. Since the start time TB2 of the secondary feed of the second paper P is delayed, the interval from the start time TB1 of the secondary feed of the first paper P to the start time TB2 of the secondary feed of the second paper P Becomes longer than the target interval (for example, longer by ΔT). Further, when the start time TB2 of the secondary feeding of the second paper P is delayed, the passing time TC2 of the second paper P is delayed and the arrival time TA3 of the third paper P is delayed. The start time TB3 of the secondary feeding of the paper P is also delayed.

  For example, the control unit 40 determines whether or not the arrival of the second paper P at the registration detection position RS is delayed. The delay determination by the control unit 40 is performed based on the output value of the paper sensor SP. When the control unit 40 determines that the arrival of the second paper P at the registration detection position RS is delayed, the control unit 40 switches the transport speed of the second paper P to the registration detection position RP to a speed higher than the normal transport speed.

  If the transport speed of the second paper P is switched to a speed faster than the normal transport speed in this way, the leading edge of the second paper P is moved until the elapsed time T from the passage time TC1 of the first paper P exceeds the threshold time Th. The registration detection position RP can be reached (the time difference T between the passage time TC1 of the first paper P and the arrival time TA2 of the second paper P does not exceed the threshold time Th). As a result, the secondary paper feed of the second paper P can be started at a constant interval (target interval) from the start of the secondary paper feed of the first paper P. Further, the start of the secondary paper feeding of the third paper P is not delayed.

  However, in some cases, even if the transport speed of the second paper P is switched to a speed faster than the normal transport speed, as shown in FIG. 3 (see the following figure), the elapsed time from the passage time TC1 of the first paper P There arises a disadvantage that the leading edge of the second sheet P cannot reach the registration detection position RP until T exceeds the threshold time Th. In this case, the start of the secondary paper feeding of the second paper P is delayed.

  In order to eliminate such inconvenience, the control unit 40 performs a speed switching process for switching the transport speed of the second paper P after the start of the secondary paper feeding of the second paper P. Specifically, as shown in FIG. 4 (see the following figure), the control unit 40 determines that the time difference T between the passage time TC1 of the first paper P and the arrival time TA2 of the second paper P exceeds the threshold time Th. The second sheet P is determined as the delayed sheet P. Then, after the start of the secondary paper feeding of the second paper P (delayed paper P), the control unit 40 switches the transport speed of the second paper P to the first transport speed higher than the normal transport speed (second paper P). High-speed conveyance for the object is performed by the conveyance unit 20). That is, the conveyance unit 20 performs high-speed conveyance of conveying the second paper P at the first conveyance speed after the start of the secondary paper feeding of the second paper P. At this time, the control unit 40 sets the first conveyance speed so as not to exceed the upper limit value of the sheet conveyance speed suitable for the drive frequency of the printing unit 30. Therefore, even if the conveyance unit 20 performs high-speed conveyance for the second paper P, the image quality of the image printed on the second paper P does not deteriorate.

  When the speed switching process is performed (when the high-speed conveyance is performed by the conveyance unit 20), the control unit 40 sets an appropriate sheet interval between the first sheet P and the second sheet P (delayed sheet P). Find the time it takes to become. Then, when the required time has elapsed from the start of the high-speed conveyance by the conveyance unit 20 (when the interval between the first sheet P and the second sheet P becomes an appropriate sheet interval), the control unit 40 performs the second sheet P. The transport speed is returned from the first transport speed to the normal transport speed.

  When the speed switching process by the control unit 40 (high-speed conveyance by the conveyance unit 20) is performed, the passage time TC2 of the second sheet P (delayed sheet P) is advanced, so that the second sheet P is secondarily fed. The time interval Ti between the start time TB2 and the passage time TC2 is narrowed. Therefore, the interval from the start time TB2 of the second paper P for the second paper feed to the start time TB3 of the second paper P for the third paper P is shorter than the target interval (shorter by ΔT). Thereby, although the start of the secondary paper feed of the second paper P is delayed, the start of the secondary paper feed of the third paper P can be prevented from being delayed (the transport delay generated in the second paper P is suppressed). Can be absorbed).

  For example, the control unit 40 recognizes the current position of the second sheet P (delayed sheet P) based on the output value of the sheet sensor PS when the conveying unit 20 is performing high-speed conveyance. Then, the control unit 40 controls the transport unit 20 based on the current position of the second paper P so that high-speed transport for only the second paper P is performed.

  As an example, it is assumed that both the first paper P and the second paper P are transported along the transport path 1B for double-sided printing. In this case, the control unit 40 maintains the rotational speed of the duplex printing conveyance roller pair 26 that nips the first sheet P at the normal conveyance speed, and the duplex printing conveyance roller pair that nips the second sheet P. Only the rotational speed of 26 is switched to the first transport speed. When the duplex printing conveyance roller pair 26 that nips the first sheet P and the duplex printing conveyance roller pair 26 that nips the second sheet P are driven by the same duplex printing motor M5, For example, the control unit 40 controls on / off of the double-sided printing clutch, whereby the connection between the one-sided double-sided printing conveyance roller pair 26 and the double-sided printing motor M5 is released. The same control is performed for the carry-out side conveyance roller pair 25.

  The controller 40 determines whether or not the arrival of the single-sided printing paper P returned from the double-sided printing conveyance path 1B to the main conveyance path 1A to the registration detection position RP is delayed during double-sided printing. to decide. If the control unit 40 determines that the arrival of the single-sided printing paper P at the registration detection position RP is delayed, the control unit 40 determines that the single-sided printing paper P at which the arrival at the registration detection position RP is delayed is a delayed paper P, and performs single-sided printing. The conveyance unit 20 is caused to perform high-speed conveyance for the sheet P (delayed sheet P).

  In double-sided printing, single-sided printing is performed without printing a back image on the other side (unprinted side) opposite to one side of the single-sided printing paper P returned from the double-sided printing conveyance path 1B to the main conveyance path 1A. The paper P may be discharged. When the control unit 40 determines that the single-sided printing paper P returned from the double-sided printing conveyance path 1B to the main conveyance path 1A is the delayed paper P, the back side is placed on the other side of the single-sided printing paper P (delayed paper P). When an image is not printed, the second conveyance speed (for example, a sheet suitable for the driving frequency of the printing unit 30) that is faster than the first conveyance speed for high-speed conveyance of the single-sided printing paper P (delayed paper P) by the conveyance unit 20 is used. It may be performed at a speed exceeding the upper limit of the transport speed).

  Hereinafter, a flow of conveyance control of the paper P performed by the control unit 40 will be described with reference to a flowchart shown in FIG. The start of the flowchart shown in FIG. 5 starts when the controller 40 detects that the leading edge of the paper P reaches the registration detection position RP based on the output value of the registration sensor RS.

  In step S1, the control unit 40 detects the arrival time point when the paper P reaches the registration detection position RP based on the output value of the registration sensor RS. In step S2, the control unit 40 determines that the arrival time of the arrival paper P that has reached the registration detection position RP and the passage of the trailing edge of the preceding paper P being conveyed before the arrival paper P has passed the registration detection position RP. It is determined whether or not the time difference T from the time exceeds a predetermined threshold time Th. As a result, when the control unit 40 determines that the time difference T exceeds the threshold time Th, the process proceeds to step S3.

  In step S <b> 3, the control unit 40 determines that the arrival paper P is the delayed paper P. In step S <b> 4, the control unit 40 causes the transport unit 20 to perform high-speed transport for the delayed paper P. That is, the transport unit 20 transports the delayed paper P at a speed higher than the normal transport speed after the start of the secondary paper feeding of the delayed paper P.

  In step S5, the control unit 40 obtains the time required until the interval between the preceding sheet P and the delayed sheet P reaches a predetermined appropriate interval, and the conveyance unit 20 performs the high-speed conveyance for the delayed sheet P as a target. It is determined whether the required time has elapsed since the start. As a result, if the control unit 40 determines that the required time has elapsed, the process proceeds to step S6. If the control unit 40 determines that the required time has not elapsed, the determination in step S5 is repeated. .

  If transfering it to step S6, the control part 40 will complete | finish the high speed conveyance for the delay paper P by the conveyance part 20 as object. That is, the control unit 40 returns the conveyance speed of the delayed paper P to the normal conveyance speed.

  When the control unit 40 determines in step S2 that the time difference T does not exceed the threshold time Th, the process proceeds to step S7. In step S7, the control unit 40 causes the arrival paper P to be conveyed at the normal conveyance speed even after the start of the secondary paper feeding.

  As described above, the image forming apparatus 100 of the present embodiment supplies the paper P from the paper feed position P1 to the main transport path 1A passing through the registration position P2 and the print position P3, and from the paper feed position P1 to the main transport path 1A. The paper P is transported from the paper feed position P1 to the registration position P2, and when the paper P reaches the registration position P2, the progress of the paper P reaching the registration position P2 is temporarily stopped. The transport unit 20 that performs the secondary paper feeding that transports the paper P that has reached the registration position P2 to the print position P3, the printing unit 30 that prints an image on the paper P at the print position P3, and the transport of the paper P by the transport unit 20 When the conveyance and printing unit 30 controls the printing of the image on the paper P and causes the conveyance unit 20 to carry out continuous conveyance of a plurality of sheets, the secondary paper feeding is performed between predetermined targets. And a control unit 40 that controls the conveyance of the paper P by the conveyance unit 20 and a position upstream of the registration position in the paper conveyance direction in the main conveyance path 1A as the detection position RP, and the paper P at the detection position RP. A registration sensor RS for detecting the presence or absence. Based on the output value of the registration sensor RS, the control unit 40 detects the arrival time point of the arrival paper P that has reached the detection position RP and reaches the detection position RP, and the rear end of the preceding paper P being conveyed before the arrival paper P When the time difference between the passage time when the paper passes the detection position RP and the arrival time of the arrival paper P exceeds a predetermined threshold time, a determination process for determining the arrival paper P as the delay paper P is performed, and the arrival paper P is delayed. If it is determined that the sheet P is used, the conveyance unit 20 is caused to perform high-speed conveyance for conveying the delayed sheet P at a first conveyance speed higher than a predetermined normal conveyance speed after the start of the secondary feeding of the delayed sheet P.

  In this configuration, when the arrival paper P that has reached the detection position RP of the registration sensor RS is the delayed paper P, the transport unit 20 performs high-speed conveyance for the delayed paper P, so the secondary paper feeding of the delayed paper P is performed. The time from the start of the delay paper P until the trailing edge of the delayed paper P passes the detection position RP of the registration sensor RS (the time from the start to the end of the secondary paper feed of the delayed paper P) is shortened. For this reason, the time when the secondary paper feeding of the delayed paper P is started and the time when the secondary paper feeding of the next paper P (the paper P to be transported from the registration position P2 to the printing position P3 next to the delayed paper P) is started, and Can be made shorter than the target interval. As a result, even if the arrival of the paper P at the detection position RP of the registration sensor RS is delayed, it can be suppressed that the time taken until the final printed paper P is discharged (productivity decreases). Can be suppressed).

  Further, in the present embodiment, as described above, when the transport unit 20 causes the transport unit 20 to perform high-speed transport, the control unit 40 has a predetermined proper paper space between the preceding paper P and the delayed paper P. The required time for the paper P is obtained, and when the required time has elapsed from the start of the high-speed conveyance by the conveyance unit 20, the conveyance speed of the delayed paper P is returned to the normal conveyance speed. Thereby, it is possible to suppress the rear end portion of the preceding paper P and the front end portion of the delayed paper P from overlapping.

  In the present embodiment, as described above, the control unit 40 performs determination processing on the single-sided printing paper P returned from the double-sided printing conveyance path 1B to the main conveyance path 1A when performing double-sided printing. When it is determined that the single-sided printing paper P is the delayed paper P, the conveyance unit 20 is caused to perform high-speed conveyance for the single-sided printing paper P determined as the delayed paper P. Thereby, even when double-sided printing is performed, it is possible to suppress a decrease in productivity due to the occurrence of a conveyance delay.

  This is a case where the single-sided printing paper P returned from the double-sided printing conveyance path 1B to the main conveyance path 1A is determined by the delayed paper P and the control unit 40, and the single-sided printing paper P determined by the control unit 40 as the delayed paper P. In the case where an image is not printed on the other side opposite to the first side, it is not necessary to consider the drive frequency of the printing unit 30, and therefore, a high-speed target for delayed paper P (single-sided printing paper P) by the transport unit 20. The conveyance can be performed at a higher conveyance speed. Accordingly, when the image is not printed on the other side of the single-sided printing paper P determined as the delayed paper P, the control unit 40 causes the high-speed conveyance by the conveyance unit 20 to be performed at the second conveyance speed that is faster than the first conveyance speed.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown not by the description of the above-described embodiment but by the scope of claims for patent, and further includes meanings equivalent to the scope of claims for patent and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1A Main conveyance path 1B Duplex printing conveyance path 20 Conveyance section 30 Printing section 40 Control section 100 Image forming apparatus P1 Paper feed position P2 Registration position P3 Printing position RP Registration detection position (detection position)
RS resist sensor

Claims (4)

A main transport path from the paper feed position through the registration position and print position;
The primary paper feeding is performed to feed the paper from the paper feed position to the main transport path, the paper is transported from the paper feed position to the registration position, and reaches the registration position when the paper reaches the registration position. A transport unit that performs secondary paper feeding for transporting the paper that has reached the registration position to the printing position after stopping the progress of the paper that has been performed;
A printing unit for printing an image on a sheet at the printing position;
When controlling the conveyance of the sheet by the conveyance unit and the printing of the image on the sheet by the printing unit and causing the conveyance unit to continuously convey a plurality of sheets, the secondary paper feeding is a predetermined target. A control unit for controlling conveyance of the sheet by the conveyance unit so as to start at intervals;
A position on the upstream side in the paper conveyance direction from the registration position in the main conveyance path as a detection position, and a registration sensor for detecting the presence or absence of paper at the detection position,
The control unit detects the arrival time of the arrival paper that has reached the detection position based on the output value of the registration sensor, and the trailing edge of the preceding paper conveyed before the arrival paper is When the time difference between the passage time passing through the detection position and the arrival time exceeds a predetermined threshold time, a determination process is performed to determine the arrival paper as a delay paper, and the arrival paper is determined as the delay paper, Image forming is characterized in that after the start of the secondary feeding of the delayed paper, the transport unit performs high-speed transport for transporting the delayed paper at a first transport speed that is faster than a predetermined normal transport speed. apparatus.   The control unit obtains a time required for a gap between the preceding sheet and the delayed sheet to become a predetermined appropriate sheet interval when the conveyance unit performs the high-speed conveyance, and the conveyance unit 2. The image forming apparatus according to claim 1, wherein when the required time elapses from the start of the high-speed conveyance, the conveyance speed of the delayed sheet is returned to the normal conveyance speed. A double-sided printing conveyance path that branches off from the main conveyance path at a position downstream of the printing position in the sheet conveyance direction and merges with the main conveyance path at a position upstream of the detection position in the sheet conveyance direction;
When carrying out double-sided printing, the carrying unit pulls the single-sided printing paper having an image printed on one side at the printing position into the double-sided printing carrying path, and reverses the orientation of the front and back sides of the single-sided printing paper. After performing the reversal process, the single-sided printing paper is returned to a position upstream of the detection position of the main conveyance path in the paper conveyance direction, and the single-sided printing paper is conveyed again along the main conveyance path,
The control unit performs the determination process on the single-sided printing paper returned from the double-sided printing conveyance path to the main conveyance path when performing the double-sided printing, and determines the single-sided printing paper as the delayed paper. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus causes the conveyance unit to perform the high-speed conveyance for the single-sided printing sheet determined to be the delayed sheet.   The control unit determines that the single-sided printing paper returned from the double-sided printing conveyance path to the main conveyance path is the delayed paper, and the one side of the single-sided printing paper determined to be the delayed paper 4. The image forming apparatus according to claim 3, wherein when the image is not printed on the other side opposite to the first side, the high-speed conveyance by the conveyance unit is performed at a second conveyance speed higher than the first conveyance speed. 5. .