JP4246014B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine, and more particularly to an image forming apparatus having a double-sided printing function (double-sided printing unit).

  In general, when performing duplex printing in an image forming apparatus having a duplex printing function, a recording sheet (hereinafter simply referred to as a sheet) is fed from a sheet feeding device to an image forming unit (image forming unit) to form an image. After the image is formed on one side of the sheet by the unit, fixing is performed and the sheet is sent to the duplex printing unit. Then, the duplex printing unit reverses the sheet and feeds the sheet again to the image forming unit. The image forming unit forms an image on the other side of the sheet, and the sheet is discharged to a discharge tray after fixing.

  By the way, when an image is formed on a sheet by the image forming unit, the sheet is temporarily held by a registration roller provided on the upstream side of the image forming unit, and the sheet is driven by a registration roller according to a predetermined image writing timing. Is sent to the image forming unit. In double-sided printing, the paper on which image formation has been performed on one side as described above is reversed and sent to the image forming unit by the double-sided printing unit. The time during which the sheet is held by the roller becomes long (that is, the image writing timing is delayed).

  On the other hand, even when the image writing timing is delayed by the registration roller, a sheet with an image formed on one side is fed from the duplex printing unit, and the sheet interval (between sheets) is narrowed. In the worst case, there is a problem that the subsequent sheet catches up with the previous sheet.

  In order to prevent such inconveniences, the paper control is performed so that the paper on which the image formation on the other side is scheduled after finishing the image formation on only one side is scattered in the conveyance path, and the other side sequentially When the image is formed on the sheet, the number of scattered sheets is set to 2 or more, the feeding means in the conveyance path can be freely stopped, and when a delay in processing or transmission of image data occurs, the sheet is not in the conveyance path. There is one in which the feeding of the recording paper by the feeding means is stopped so as to be scattered, and the feeding of the feeding means is resumed after waiting for recovery of the delay (see Patent Document 1).

Japanese Patent No. 29563030 (pages 4 to 5, FIGS. 8 to 10)

  As described above, in Japanese Patent Application Laid-Open No. 2004-260260, when a delay occurs during double-sided printing, the feeding of the paper that is being transported is stopped and the paper feeding is resumed after the delay is recovered, but the paper feeding is stopped. If this happens, the paper may become dirty at the feed roller nip, and the paper may be damaged by nip marks on the paper.

  In addition, once the paper feed is stopped, when the paper feed is resumed, not only paper slip may occur at the feed roller, but also the paper feed timing is shifted due to the time lag when the drive system is restarted, which is good Image formation may not be possible.

  In any case, the conventional image forming apparatus has a problem that it is difficult to perform good image formation because paper feeding is temporarily stopped.

Therefore, in view of the problems of the prior art, the present invention adjusts and controls the conveyance speed of the recording sheet conveyed through the duplex printing unit when performing duplex printing, and the registration unit that sends the recording sheet to the image forming unit. An object of the present invention is to provide an image forming apparatus capable of controlling the sending timing and performing good image formation.

Accordingly, in order to solve the above problems, the present invention fixes an image forming unit that forms an image on a recording sheet and the recording sheet that is arranged on the downstream side of the image forming unit and on which an image is formed by the image forming unit. An image forming apparatus comprising: a fixing unit that performs printing; and a duplex printing unit that receives a recording sheet on which an image is formed on one side through the fixing unit, and reverses the surface of the recording sheet and sends the recording sheet to the image forming unit And determining means for determining whether or not there is an image waiting time by determining whether or not the image formation by the image forming unit is delayed from a predetermined timing, and the both sides according to the image waiting time a transport speed adjustment control means for adjusting the control to decrease the conveying speed of the recording sheet conveyed in the printing unit without stopping the image forming Yoo It characterized in that it has a timing control means for controlling the transmission timing of the registration unit for sending the recording paper to Tsu and.

  In the present invention, when a predetermined number of recording sheets are fed for each recording sheet size and then the first recording sheet is conveyed to the duplex printing unit, the control by the conveyance speed adjustment control means is performed. Is started, and when another sheet of recording paper is supplied to the image forming unit following the predetermined number of sheets, control by the timing control unit is started.

As described above, the image forming apparatus of the present invention determines whether there is an image waiting time by determining whether image formation by the image forming unit is delayed from a predetermined timing. Adjustment control is performed so as to decrease without stopping the conveyance speed of the recording paper conveyed through the duplex printing unit according to the waiting time, and the timing of sending the registration unit that sends the recording paper to the image forming unit is controlled. than in the, there is an effect that it is possible to perform a good good image formation.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a diagram schematically illustrating an example of an image forming apparatus according to the present invention. The illustrated image forming apparatus includes four sheet feeding apparatuses 11 to 14. The paper is selectively sent to the paper transport path P. A registration roller pair 21 is disposed in the sheet conveyance path P, and an image forming unit (image forming unit) 22 is positioned on the downstream side of the registration roller pair 21 (in FIG. 1, the image forming unit 22 is photosensitive). Only the body drum 22a and the transfer belt 22b are shown).

  Further, a fixing unit 23 is disposed on the downstream side of the image forming unit 22, and the sheet conveyance path P is branched into two paths on the exit side of the fixing unit 23. One route is a paper discharge route Q, and the other route is a route to the duplex printing unit 31 (hereinafter, this route is referred to as a first branch route R). The paper transport path P is selectively connected to the paper discharge path Q and the first branch path R.

  The first branch path R is continuous with the refeeding section 32, and the refeeding section 32 is continuous with the second branch path S and the reversing path T via the reversing roller 33, and refeeds. The unit 32 is selectively connected to the second branch path S and the inversion path T. The second branch path S is connected to the paper discharge path Q, and the reverse path T is connected to the paper transport path P on the upstream side of the registration roller pair 21.

  As shown in the figure, in the paper transport path P, first and second transport roller pairs 41 and 42 are disposed upstream of the registration roller pair 21, and a third transport roller is disposed on the exit side of the fixing unit 23. A pair 43 is arranged. The first branch path R is provided with fourth and fifth transport roller pairs 44 and 45, and the refeed unit 32 is provided with a refeed roller 32a. Further, the reverse path T is provided with first to third reverse conveying rollers 51 to 53. The second branch path S is provided with a sixth transport roller pair 46, and the paper discharge path 47 is provided with a paper discharge roller 47.

  As shown in FIG. 1, a registration switch (registration SW) 60 is disposed in the vicinity of the registration roller pair 21 on the upstream side of the registration roller pair 21, and the first paper detection SW 61 is provided in the refeed unit 32. Has been placed. Further, a second paper detection SW 62 is disposed in the vicinity of the reversing roller 33, and third to fifth paper detection SWs 63 to 65 are disposed on the entry sides of the first to third reverse conveying rollers 51 to 53, respectively. Has been.

  Although there are other paper detection SWs, they are omitted in FIG. 1 because they are not directly related to the present invention. Then, in response to the sheet detection signals from the registration SW 60 and the first to fifth sheet detection SWs 61 to 65, the control device (not shown), as will be described later, the registration roller pair 21 and the refeed roller 32a. The reversing roller 33 and the first to third reversing conveying rollers 51 to 53 are driven and controlled (in FIG. 1, driving motors for driving the respective rollers are omitted).

  During single-sided printing, the paper on which an image is formed on one side by the image forming unit 22 passes through the fixing unit 23 and is discharged from a paper discharge path Q to a paper discharge tray by a paper discharge roller 47 (at this time) Is discharged with the printing surface facing upward (that is, discharged with face-up)). During face-up printing, when face-up is selected so that the paper is discharged with the printing surface facing downward, the paper that has come out of the fixing unit 23 is sent to the first branch path R and reaches the refeed unit 32. Then, the paper refeed roller 32 a is driven, the paper is conveyed to the second branch path S, and is discharged to the paper discharge tray face down by the paper discharge roller 47.

  On the other hand, at the time of duplex printing, the sheet on which an image is formed on one side is sent from the fixing unit 23 to the first branch path R and reaches the refeed unit 32. Then, the refeed roller 32 a is driven and the reversing roller 33 is driven, so that the sheet is reversed and conveyed to the reversing path T. As shown in FIG. 1, the reverse path T is connected to the paper transport path P on the upstream side of the first transport roller pair 41, and the paper that has exited the reverse path T passes through the paper transport path P and the image forming unit. 22, where after an image is formed on the other side of the sheet, the sheet passes through the fixing unit 23 and is discharged from the discharge path Q to the discharge tray.

  Here, with reference to FIG. 2 as well, paper conveyance control during double-sided printing will be described (note that the paper is transferred from the registration roller pair 21 to the image forming unit 22 at a predetermined writing timing (hereinafter referred to as a fixed timing). Shall be sent). Now, when a print command (this print command includes at least information indicating the print size and double-sided printing) is given from an operation panel (not shown) provided in the image forming apparatus (step S1). ) After recognizing the print size (step S2), the control device determines whether or not double-sided printing (double-sided printing) is performed (step S3). If it is not double-sided printing in step S3, the control device starts single-sided printing (step S4).

  On the other hand, in the case of duplex printing in step S3, the control device circulates to the image forming apparatus according to a preset paper size (print size) (circulation number (number determined in advance for each paper size)). To decide. In other words, in the storage device (memory: not shown), the circulation number for each paper size is preset as a circulation number table, and for double-sided printing, the control device refers to the circulation number table (step S5). ) The number of circulating sheets is determined according to the print size input from the operation panel (step S6). Here, for example, the number of circulating sheets is set to 2 for the A3 size and the B4 size, 3 for the A4 vertical size and the B5 vertical size, and the like.

  When the circulation number is determined as described above, the first sheet is fed from any of the sheet feeding devices 11 to 14 to the registration roller pair 21 via the sheet conveyance path P (first sheet feeding). Start: Step S7). When the registration SW 60 is turned on (when paper is detected), the control device determines whether or not the writing start timing is delayed from the fixed timing due to the delay of the image data processing (that is, whether or not there is an image waiting time). Determination: Step S8) If there is no image waiting time, the printing process is performed at a fixed timing (Step S9).

  On the other hand, if there is an image waiting time, the control device adjusts the delay time (step S10). That is, the control device controls the driving of the registration roller pair 21 and the first and second transport rollers 41 and 42 to adjust the delay time according to the image waiting time (the registration roller pair 21 and the first and first transfer rollers). 2), the paper is supplied to the image forming unit 22. Thereafter, the sheets are sequentially fed from the second sheet to the circulation number (step S11), and the processes of steps S8 to S10 are performed for each sheet until the circulation number of sheets is fed (step S12).

  When sheets from the second sheet to the circulating sheet are fed (step S12), the control device sets m = 1 (step S13). At this time, the first sheet is sent to the refeed unit 32 and is conveyed to the reversing path T as described above, and the first sheet is in a waiting state for printing on the other side (back side) (step S14). ). Here, again, the control device determines whether or not there is an image waiting time (step S15), and if there is no image waiting time, performs a printing process at a fixed timing (step S16).

  In step S <b> 14, when image waiting time is present when performing printing on the other side of the first sheet, the control device drives and controls the reverse roller 33 and the first to third reverse conveyance rollers 51 to 53. The conveyance speed of the first sheet is reduced according to the image waiting time (delay time adjustment: step S17). Thereafter, the nth sheet (n is an integer equal to or greater than the number of circulations + 1) is fed from any of the sheet feeding devices 11 to 14 (step S18), and the first sheet is fed from the reverse path T to the sheet transport path P. (In this case, the nth sheet passes through the image forming unit 22).

  Then, the control device again determines whether there is an image waiting time for the first sheet (step S19). If there is no image waiting time, the printing process is performed at a fixed timing (step S20). If there is a waiting time, the registration roller pair 21 is controlled, and the first sheet conveyance timing is set according to the image waiting time. (Delay time adjustment: step S21). Thereafter, the control device sets m = m + 1 (step S22), and steps S14 to S21 are sequentially performed for the (1 + m) th sheet (m is an integer equal to or greater than 1).

As described above , adjustment control is performed so as to decrease without stopping the conveyance speed of the sheet sent to the duplex printing unit 31 according to the image waiting time, and adjustment control of the sheet feeding by the registration roller pair 21 is performed. since the, the delay in the image data processing is generated, so that it is possible to perform a good good image formation.

  As is apparent from the above description, the control device functions as a determination unit, a conveyance speed adjustment control unit, and a timing control unit.

It is determined whether or not image formation by the image forming unit is behind a predetermined timing to determine whether or not there is an image waiting time, and the recording that is conveyed in the duplex printing unit according to the image waiting time Since the paper conveyance speed is adjusted and controlled, and the sending timing of the registration unit for sending the recording paper to the image forming unit is controlled , the invention can be applied to a copying machine, a printer, a copying machine or the like having a duplex printing unit.

1 is a diagram illustrating Embodiment 1 of an image forming apparatus according to the present invention. 3 is a flowchart for explaining sheet conveyance control in the image forming apparatus shown in FIG. 1.

Explanation of symbols

11 to 14 Paper feeder 21 Registration roller pair 22 Image forming unit (image forming unit)
23 Fixing unit 31 Duplex printing unit 32 Refeed unit 33 Reverse rollers 51-53 Reverse transport roller 60 Registration switch 61-65 Paper detection switch

Claims (3)

An image forming unit that forms an image on a recording sheet; a fixing unit that is disposed downstream of the image forming unit and that fixes the recording sheet on which an image is formed by the image forming unit; and passes through the fixing unit. An image forming apparatus having a duplex printing unit that receives a recording sheet on which an image is formed on one side, and reverses the surface of the recording sheet and sends the recording sheet to the image forming unit.
Determining means for determining whether image formation by the image forming unit is delayed from a predetermined timing and determining whether there is an image waiting time;
A conveyance speed adjustment control means for adjusting and controlling the conveyance speed of the recording paper conveyed through the double-sided printing unit so as to decrease without stopping according to the image waiting time;
An image forming apparatus comprising: a timing control unit that controls a sending timing of a registration unit that sends the recording paper to the image forming unit.   After a predetermined number of recording sheets are fed for each recording sheet size, when the first recording sheet is conveyed to the duplex printing unit, the control by the conveyance speed adjustment control unit starts. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   3. The image according to claim 2, wherein when the recording sheet is supplied to the image forming unit after the predetermined number of sheets, the control by the timing control unit is started. Forming equipment.

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