JP6218890B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus capable of performing double-sided printing.

  In recent years, the resolution of printers has been increased, and printers with a resolution of 600 dpi (dots / inch) and 1200 dpi have appeared. In such a printer, switching between 600 dpi and 1200 dpi is realized by changing the conveyance speed of the recording paper (sheet). That is, assuming that the sheet conveyance speed at 600 dpi is the first constant speed, printing at twice the resolution is realized by conveying the sheet at half the first constant speed (half speed) at 1200 dpi. ing. As described above, when printing at 1200 dpi, the sheet conveyance speed is halved, so that the productivity is halved. However, in order to realize 1200 dpi printing at the first constant speed, the hardware cost increases, such as doubling the number of rotations of the polygon mirror that scans the laser beam or doubling the number of laser beams. Therefore, in order to realize low-cost and high-resolution printing, switching of the resolution by switching of the conveyance speed is an indispensable technique, and has been proposed in, for example, Patent Document 1 and Patent Document 2 and the like.

  On the other hand, as a method for forming images on both the front and back surfaces of a large number of sheets, there is a method that uses a circulation type paper conveyance system. This is because the sheet is sent to the transfer part to transfer the image, the image is printed on one side of the sheet, the sheet is further sent to the reversing part, and the reversed sheet is sent again to the transfer part to the opposite side. This is a method of printing an image on both sides of a sheet by transferring the image. In order to improve productivity by closing the gap between papers, instead of feeding and refeeding a single sheet of paper for double-sided printing, a plurality of sheets are fed together to form an image on the first side. After printing continuously, the sheet on which the image is printed on the first side is sent to the duplex path. Thereafter, double-sided circulation control is performed in which an image on the first side of a newly fed sheet and an image on the second side of the sheet conveyed via the double-sided path are printed alternately.

  As an image forming apparatus using such a circulation type paper conveyance system, Patent Document 3 is proposed in which the number of double-sided circulation sheets is determined according to the paper size and paper type of a sheet to be fed. Further, even if there is a sheet to be printed subsequently, if there are certain conditions, the control for interrupting the double-sided circulation is performed once. For example, when the paper size is switched from A4 to A3, the double-sided circulation is interrupted. This is because the circulation number is switched depending on the paper size and paper type. Also, when the paper type (plain paper to thick paper) is switched, the double-sided circulation is interrupted because the transport speed is switched.

JP 2000-181275 A JP 2002-23576 A Japanese Patent No. 03767855

  The conventional double-sided circulation control of a sheet in Patent Document 3 is controlled in units of sheets. This is because the double-sided circulation number is obtained from sheet information such as “paper size” and “paper type”. On the other hand, the sheet conveyance speed is also switched depending on the “paper type”. This is because a sheet having a large basis weight, such as thick paper, increases the heat capacity and realizes stable fixing by slowing the conveying speed.

However, Japanese Patent Laid-Open No. 2004-228688 determines whether double-sided circulation is interrupted according to sheet information such as “paper size” and “paper type”, and does not determine whether double-sided circulation is interrupted based on resolution. For this reason, when images having different resolutions are recorded on a plurality of recording papers, the double-sided circulation can not be appropriately interrupted even though the conveyance speed changes between the recording papers.

  The present invention has been made to solve the above problems.

An object of the present invention, when performing duplex printing on a plurality of sheets of recording paper, in accordance with the resolution of the image formed on the recording paper of their respective properly interrupt the double-sided circulation to perform duplex printing It is to provide the technology that can.

The present invention is, for example, an image forming apparatus that includes an image forming unit that forms an image on a sheet, a sheet feeding unit that feeds a sheet, and a sheet fed from the sheet feeding unit to the image forming unit. If the resolution of the image formed by the image forming unit is the first resolution, the sheet is transported to the image forming unit at a first transport speed and formed by the image forming unit. When the image resolution is a second resolution higher than the first resolution, the conveyance unit conveys the sheet to the image forming unit at a second conveyance speed lower than the first conveyance speed; and the image A double-sided circulation path for reversing the front and back of the sheet that has passed through the forming unit and refeeding the image forming unit, and feeding a plurality of sheets continuously from the sheet feeding unit, the first of each sheet After the image is formed on the surface, the image is Double-sided circulation in which an image forming process is alternately performed on the second surface of the sheet re-fed to the forming unit and an image forming process is performed on the first surface of the sheet newly fed from the sheet feeding unit. Control means for executing control, wherein the control means has a resolution of an image formed on a first surface of a first sheet conveyed from the paper feeding unit to the image forming unit, and the first The resolution of the image formed on the first surface of the second sheet conveyed from the paper feeding unit to the image forming unit one after the sheet is the same , and formed on the second surface of the first sheet When the resolution of the image to be processed and the resolution of the image formed on the first surface of the second sheet are the same, the double-sided circulation control is continued, and the image is displayed on the second surface of the first sheet. Before forming, the second sheet is conveyed from the sheet feeding unit to the image forming unit, and the first sheet If the resolution of the image formed on the first surface of the resolution and the second sheet of image to be formed on the first surface of the over bets are different, or, the image formed on the second surface of the first sheet If the resolution of the image and the resolution of the image formed on the first surface of the second sheet are different , the double-sided circulation control is interrupted and the second image is formed after the image is formed on the second surface of the first sheet. The sheet is conveyed from the sheet feeding unit to the image forming unit.

According to the present invention, when performing duplex printing on a plurality of sheets of recording paper, in accordance with the resolution of the image to be recorded on the recording paper of their respective properly interrupt the double-sided circulation to perform duplex printing The effect is that

1 is a block diagram showing an overall configuration of an image input / output system to which an image forming apparatus (multifunction peripheral) according to an embodiment of the present invention can be applied. Sectional drawing explaining the structure of a reader part and a printer part. FIG. 3 is a top view of the operation unit according to the first embodiment. FIG. 4 is a schematic diagram illustrating a sheet conveyance state in a printer unit. FIG. 6 is a diagram illustrating a sheet conveying method for performing single-sided printing. FIG. 5 is a diagram illustrating a sheet conveying method for performing duplex printing. FIG. 6 is a schematic diagram for explaining a sheet conveyance method when performing circulation double-side printing. FIG. 3 is a schematic diagram illustrating a paper feeding order when a circulating image is formed in the image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating an example of a table for obtaining a circulation number and a conveyance speed from a paper size, a paper type, and a resolution in the image forming apparatus according to the first embodiment. FIG. 4 is a diagram for explaining paper (sheet) used for printing, its size, paper type, images printed on both sides of each sheet, and resolution. FIG. 10 is a diagram illustrating sheet conveyance control of a conventional image forming apparatus. FIG. 4 is a diagram illustrating sheet conveyance control of the image forming apparatus according to the first embodiment. 6 is a flowchart for describing conveyance control processing by a sheet control unit of the image forming apparatus according to the first embodiment. 14 is a flowchart for explaining a determination process for determining whether to interrupt double-sided circulation in S104 of FIG. FIG. 3 is a diagram illustrating an example of paper (sheet) output by the image forming apparatus according to the first embodiment. FIG. 3 is a diagram for explaining the order of sheets fed and re-fed by the image forming apparatus according to the first embodiment. The figure which shows an example of the double-sided imposition in Embodiment 2. FIG. 9 is a diagram for explaining the order of sheets fed and re-fed by the image forming apparatus according to the second embodiment. 9 is a flowchart for explaining double-sided layout processing by a control unit of the image forming apparatus according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the present invention. .

[Embodiment 1]
FIG. 1 is a block diagram showing an overall configuration of an image input / output system (printing system) to which an image forming apparatus (multifunction machine) according to an embodiment of the present invention can be applied.

  A reader unit (image input device) 200 optically reads a document image and converts it into image data. The reader unit 200 includes a scanner unit 210 having a function for reading a document, and a document feeding unit (DF unit) 250 having a function for conveying a document to be read.

  A printer unit (image output apparatus) 300 conveys a sheet, prints image data as a visible image on the sheet, and discharges the sheet outside the apparatus. The printer unit 300 includes a paper feed unit 310 having a plurality of types of sheet cassettes, a marking unit 320 having a function of transferring and fixing image data to a sheet, and a paper discharge unit 330 having a function of outputting printed sheets to the outside of the apparatus. It is equipped with.

  The control unit 110 includes a CPU 120, an image memory 130, a nonvolatile memory 140, a RAM 150, a ROM 160, and an operation unit 170. The control unit 110 is electrically connected to the reader unit 200 and the printer unit 300. Then, the CPU 120 in the control unit 110 controls the reader unit 200 to read the image data of the document into the image memory 130, and controls the printer unit 300 to output the image data in the image memory 130 to a sheet and copy function. I will provide a. Furthermore, various adjustment values are stored in the nonvolatile memory 140, the RAM 150 is used as a work area for the CPU 120, and the control program for the CPU 120 is stored in the ROM 160. The operation unit 170 includes an LCD touch panel 360 (FIG. 3) including a liquid crystal display unit and a touch panel attached to the liquid crystal display unit, and a plurality of hard keys. A signal input by the touch panel or the hard key is transmitted to the CPU 120, and a function display, image data, and the like in the operation of the image forming apparatus are displayed on the liquid crystal display unit.

  FIG. 2 is a cross-sectional view illustrating the configuration of the reader unit 200 and the printer unit 300.

  First, the reader unit 200 will be described.

  In the reader unit 200, a document feeding unit (feeder) 250 feeds the documents one by one from the top to the platen glass 211 in order, and after the document reading operation is completed, the documents on the platen glass 211 are discharged to the discharge tray 219. To discharge. When the document is conveyed onto the platen glass 211, the lamp 212 is turned on, and the movement of the optical unit 213 is started, and the document is exposed and scanned. Reflected light from the original at this time is guided to a CCD image sensor (hereinafter referred to as CCD) 218 by mirrors 214, 215, 216 and a lens 217. Thus, the scanned image of the original is read by the CCD 218. Image data output from the CCD 218 is transferred to the control unit 110 after being subjected to predetermined processing.

  Next, the printer unit 300 will be described.

  The laser driver 321 drives the laser emission unit 322 to cause the laser emission unit 322 to emit laser light corresponding to the image data output from the control unit 110. The laser beam is irradiated onto the photosensitive drum 323 via a polygon mirror, and a latent image corresponding to the laser beam is formed on the surface of the photosensitive drum 323. A developer is attached to the latent image portion of the photosensitive drum 323 by a developing device 324.

  In addition, the printer unit 300 includes a paper feed cassette 311, a paper feed cassette 312, a paper feed cassette 313, and a paper feed cassette 314 each having a drawer shape as a paper feed unit. Further, the paper feed unit 310 has a manual paper feed tray 315. The printer unit 300 feeds a sheet from any one of the sheet feeding cassettes 311, 312, 313, 314 and the manual sheet feeding tray 315, and conveys the sheet to a transfer unit (printing unit) 325 through a conveyance path 331. The transfer unit 325 transfers the developer attached to the photosensitive drum 323 to a sheet. Thus, the sheet with the developer attached is conveyed to the fixing unit 327 by the conveying belt 326, and the developer is fixed to the sheet by the heat and pressure of the fixing unit 327. Thereafter, the sheet that has passed through the fixing unit 327 is discharged through the conveyance path 335 and the conveyance path 334. Alternatively, when the printing surface is reversed and discharged, the sheet is guided to the conveyance path 336 and the conveyance path 338, and then the sheet is conveyed in the reverse direction and passes through the conveyance path 337 and the conveyance path 334. If duplex printing is set, the sheet passes through the fixing unit 327 and is then guided from the conveyance path 336 to the conveyance path 333 by the flapper 329. Thereafter, the sheet is conveyed in the reverse direction, and is guided by the flapper 329 to the conveyance path 338 and the refeed conveyance path 332 (circulation path). The printed sheet guided to the refeed conveyance path 332 passes through the conveyance path 331 at the timing described above and is again fed to the transfer unit 325. Regardless of single-sided or double-sided printing, the sheet discharged from the transport path 334 is transported to the paper discharge bin 350.

  Next, the operation unit 170 will be described with reference to FIG.

  FIG. 3 is a top view of the operation unit 170 according to the first embodiment.

  The LCD touch panel 360 is used by the user for main mode setting and status display. The numeric keypad 361 is used for the user to input a numerical value from 0 to 9. The ID key 362 is used when inputting the department number and the password mode when the MFP is managed. The reset key 363 is a key for resetting the set mode, and the guide key 604 is a key for displaying an explanation screen for each mode. The user mode key 365 is a key for entering the user mode screen, and the interrupt key 366 is a key for performing interrupt copying. A start key 367 is a key for starting a copy operation, and a stop key 368 is a key for stopping a copy job being executed. When the soft power SW 369 is pressed, the backlight of the LCD touch panel 360 is turned off, and the multifunction device shifts to a low power state. When the power saving key 370 is pressed, the power saving state is entered, and when the power saving key 370 is pressed again, the power saving state is restored.

  The adjustment key 371 is a key for adjusting the contrast of the LCD touch panel 360. When the counter confirmation key 372 is pressed, a count screen displaying the total number of copies used so far is displayed on the LCD touch panel 360. An LED 373 indicates that a job is being executed or an image is being stored in the image memory. An error LED 374 indicates that the multifunction device is in an error state, such as a jam or a door open. An LED 375 is a power LED indicating that the main switch of the multifunction device is ON.

  Hereinafter, with reference to FIGS. 4, 5, and 6, a sheet conveying method when performing image formation will be described.

  FIG. 4 is a schematic diagram illustrating a sheet conveyance state in the printer unit 300, and the same components as those in FIG. 2 are denoted by the same reference numerals. Note that, here, the paper feed stage is described as being limited to the manual paper feed stage 315, but the same applies to the case of the paper feed cassette 311, the paper feed cassette 312, the paper feed cassette 313, and the paper feed cassette 314.

  4 corresponds to a state where the sheet is not conveyed on the conveying path, and FIGS. 5A and 5B correspond to a sheet conveying method for performing single-sided printing.

  When performing single-sided printing, as shown in FIG. 5A, the sheet S fed from the manual paper feed stage 315 is conveyed to the transfer unit 325 through the paper conveyance path 331. Then, the sheet S on which the image is transferred (Δ in the figure indicates the transferred image) is discharged through the conveyance path 335. In this case, the transferred image is discharged upward.

  Alternatively, when the transferred image is to be discharged downward, the sheet S on which the image is transferred by the transfer unit 325 passes through the conveyance path 336 and the conveyance path 338 as shown in FIG. It is conveyed and discharged through the conveyance path 327. Thus, by switching back the sheet S on which the image is printed on one side, the transferred image can be discharged downward.

  Next, with reference to FIG. 6, a sheet conveying method when performing duplex printing will be described. FIG. 6 is a schematic diagram illustrating a sheet conveyance state when duplex printing is performed in the printer unit 300, and the same components as those in FIG. 2 are denoted by the same reference numerals. Although the paper feed stage is described as the manual paper feed stage 315 here, the same applies to the case of the paper feed cassette 311, the paper feed cassette 312, the paper feed cassette 313, and the paper feed cassette 314.

  In FIG. 6A, when an image is formed on the surface of a sheet to be printed on both sides, the sheet S fed from the manual feed stage 315 is conveyed to the transfer unit 325 through the conveyance path 331. The sheet S on which the image has been transferred (Δ in the drawing indicates the transferred surface image) is guided from the conveyance path 336 to the conveyance path 333, and then the sheet is conveyed in the reverse direction, the conveyance path 338, and the refeed conveyance. It leads to the path 332.

  Next, as shown in FIG. 6B, the sheet S on the front surface (one surface) existing in the refeed conveyance path 332 is then transferred to the conveyance path 331 at an appropriate timing. The paper is fed again and conveyed to the transfer unit 325. Then, the image is transferred to the back surface (the other surface) (the half ellipse in the figure indicates the transferred back image). The sheet S on which images are transferred on both sides passes through the conveyance path 335 and is discharged outside the apparatus.

  Hereinafter, with reference to FIG. 7, a sheet conveying method (feed control) in the case of performing circular duplex printing will be described. FIG. 7 is a schematic diagram showing a conveyance state of a plurality of sheets when the printer unit 300 performs circulating double-sided printing. The same components as those in FIG. 2 are denoted by the same reference numerals. Here, the case where the paper feed stage is the manual paper feed stage 315 will be described, but the same applies to the case of the paper feed cassette 311, the paper feed cassette 312, the paper feed cassette 313, and the paper feed cassette 314.

  FIG. 7A shows the conveyance order of sheets existing in the paper conveyance path when three sheets are circulated, and S1 to S3 in the figure indicate the conveyance order of sheets existing in the paper conveyance path.

  FIG. 7B shows the conveyance order of the sheets existing in the paper conveyance path when five sheets are circulated, and S1 to S5 in the figure indicate the conveyance order of the sheets existing in the paper conveyance path.

  Here, the number of circulating sheets mainly varies depending on the sheet size. In this case, since the length of the conveyance path is determined, a sheet having a small size can be fed in advance, so that a larger number of sheets can be circulated. On the other hand, with a large size sheet, only a small number of sheets can be fed in advance, so the number of circulating sheets decreases.

  FIG. 8 is a schematic diagram showing the paper feeding order when circulating images are formed in the image forming apparatus according to the first embodiment. FIG. 8A shows the sheet feeding order when three sheets are circulated (circulation number is 3), and FIG. 8B shows the sheet feeding order when five sheets are circulated (circulation number is 5). In the figure, numerals 1 to 5 written on the sheet indicate how many sheets the sheet is.

  As shown in FIG. 8A, in the case of performing three-sheet circulation printing by double-sided printing, after feeding the first sheet surface in 801, the back surface of the first sheet is then transferred. In step 802, the surface of the second sheet is fed. Next, at 803, the back side of the first sheet that has been fed first is re-fed, then at 804, the front side of the third sheet is fed, and at 805, the second sheet is fed. In step 806, the back side of the back side of the third sheet is fed, and the front side of the third sheet is fed. Thus, these processes are continued every three sheets.

  FIG. 8B is a diagram for explaining a case where five-sheet circulation printing is performed by double-sided printing. Here, instead of feeding the front surface of the first sheet at 810 and then feeding the back surface of the first sheet again, the front surface of the second sheet is fed at 811. To do. Further, instead of refeeding the back surface of the first sheet as in the circulation of three sheets, the front surface of the third sheet is fed at 812. Then, in step 813, the back surface of the first sheet fed first is fed again, and then in step 814, the front surface of the fourth sheet is fed. In 815, the back surface of the second sheet is fed again, and in 816, the front surface of the fifth sheet is fed. Then, after 817, the back side of the third to fifth sheets is fed again. Thus, these processes are continued every 5 sheets.

  As described above, the reason why the circulation number is changed to 3 or 5 is to efficiently perform double-sided printing with different paper sizes on the same paper path.

  FIG. 9 is a diagram showing an example of a table for determining the number of sheets that can be circulated and the conveyance speed from the paper size, paper type, and resolution in the image forming apparatus according to the first embodiment. Stored in the memory 140.

  Here, the circulation number is basically determined by the paper (sheet) size. For example, as shown in the figure, when the paper size is “A4”, the circulation number is “5”, but when the paper size is “A3”, the circulation number is “3”.

  The conveyance speed is determined by the paper type and resolution. For example, when the paper type is “plain paper” and the resolution is “600 dpi”, the conveyance speed is constant. On the other hand, when the paper type is “thick paper”, the speed is half speed. This is because the developer is fixed to the sheet by the heat and pressure of the fixing unit 327. However, if the sheet type is “thick paper” and the heat is not easily transmitted, the conveyance speed is reduced to a half speed. This is because a large amount of heat is transmitted to the sheet to realize stable fixing.

  Also, when the resolution is 1200 dpi, the transport speed is half speed. This is because the sheet conveyance speed is set to half speed, a latent image with high resolution is formed on the photosensitive drum 323 with the same number of laser beams and the rotation speed of the polygon mirror as in 600 dpi, and the transfer unit 325 forms the photosensitive drum. This is because the developer attached to the H.323 is transferred to the sheet.

  The sheet conveyance control in the conventional image forming apparatus and the image forming apparatus according to the first embodiment will be described with reference to FIGS.

  FIG. 10 is a diagram illustrating paper (sheet) used for printing, its size, paper type, images printed on both sides of each sheet, and resolution.

  Here, all of the papers A to E have the paper size “A4” and the paper type “plain paper”. The resolution of the image printed on these sheets is 600 dpi except for the paper B re-feed side (back side) (the fourth page of the original). The re-feeding side (back side) of paper B (the fourth page of the document) has a resolution of 1200 dpi. 10 to 12, the 1200 dpi print surface is represented by shading.

  FIG. 11 is a diagram illustrating sheet conveyance control of a conventional image forming apparatus. Since the paper size is “A4” and the paper type is “plain paper”, the circulation number in double-sided printing is “5” from the table of FIG.

  After feeding the paper B feed surface (the third page of the original), feed the paper C feed side (the fifth page of the original) and continue the double-sided circulation, or the paper A refeed side (the original 2nd page), the refeeding surface of paper B (the 4th page of the original) is fed again, and it is determined whether or not the double-sided circulation is interrupted. In the sheet conveyance control of the conventional image forming apparatus, the circulation number and conveyance speed in double-sided printing are obtained from the sheet size and sheet type of the sheet, and the paper B and the paper C are compared. Here, both the paper B and the paper C have the paper size “A4” and the paper type “plain paper”, so that the number of circulated sheets in double-sided printing is “5” and the transport speed is “constant speed”. Therefore, it was judged that double-sided circulation could be continued.

  However, as shown in FIG. 11, when the double-sided circulation is continued, the space between the paper D feeding surface (page 7 of the original document) 1100 and the paper E feeding surface (page 9 of the original document) 1101 whose conveyance speed is “constant speed”. In addition, there is printing on the re-feeding surface 1102 of the paper B having the conveyance speed of “half speed”.

  When this is applied to FIG. 7B illustrating the conveyance control of the circulation of five sheets by duplex printing, the sheet S4 is the front surface 1100 of the paper D, the sheet S2 is the paper B (back surface) 1102, and the sheet S5 is the front surface 1101 of the paper E. It becomes. In this state, when the transport speed of the paper B refeeding surface (the fourth page of the original) (S2) becomes half speed, the transport speed of the subsequent paper E feeding surface (the ninth page of the original) (S5) is constant. Therefore, the paper E (S5) catches up with the paper B (S2), the paper E and the paper B collide, and a jam occurs.

  FIG. 12 is a diagram illustrating sheet conveyance control of the image forming apparatus according to the first embodiment.

  After feeding the paper B feeding surface (page 3 of the original), feed the paper C feeding side (page 5 of the original) and continue the double-sided circulation, or the paper A refeeding side (original) 2nd page), the refeeding surface of paper B (the 4th page of the original) is refeeded, and it is determined whether or not the double-sided circulation is interrupted. This determination is made by the control unit 110. At that time, in the sheet conveyance control of the first embodiment, the conveyance speed is obtained based not only on the sheet size and sheet type of the sheet but also on the resolution of the printing surface (conveyance speed determination). That is, not only double-sided circulation in units of paper but also the conveyance speed of the printing surface is compared to determine whether double-sided circulation is to be continued or interrupted.

  Specifically, the paper C feeding surface (the fifth page of the original) 1202 and the paper B feeding surface (the third page of the original) 1201 are compared. Here, since the paper size is “A4” and the paper type is “plain paper”, the number of double-sided circulations is “5” from the table of FIG. Further, since the resolution is also 600 dpi, it is “constant speed” from the table of FIG.

  Next, the paper C feeding surface (5th page of original document) 1202 and the paper B refeeding surface (4th page of original document) 1204 are compared. In this case, since the paper size is “A4” and the paper type is “plain paper” in both cases, the double-sided circulation number is “5” from the table of FIG. However, since the resolution of the paper C feeding surface (5th page of the original) 1202 is 600 dpi, the conveyance speed is “constant speed”, but the resolution of the paper B refeeding side (4th page of the original) 1204 is 1200 dpi. Therefore, the conveyance speed is “half speed”. As a result, it is determined that the double-sided circulation cannot be continued because the conveyance speeds do not match, and once the double-sided circulation is interrupted and all the paper (paper A and paper B) is discharged from the device, paper C is fed. To do.

  FIG. 13 is a flowchart illustrating a conveyance control process performed by the sheet control unit 110 of the image forming apparatus according to the first embodiment. Note that a program for executing this processing is stored in the ROM 160, developed in the RAM 150, and executed under the control of the CPU 120.

  This process is started when the control unit 110 starts sheet conveyance control. First, in step S101, the control unit 110 determines whether the double-sided circulation interruption flag of the RAM 150 is on or off. If the double-sided circulation interruption flag is on, the process proceeds to S112, and if it is off, the process proceeds to S102. In S102, the control unit 110 confirms whether there is a sheet (sheet) waiting to be fed. If there is paper waiting to be fed, the process proceeds to S103, and if not, the process proceeds to S112.

  In S103, the control unit 110 determines whether there is a paper waiting for refeeding. If there is no paper waiting for refeeding, the control unit 110 proceeds to S110, and if present, proceeds to S104. In step S110, the control unit 110 confirms whether or not the leading sheet waiting to be fed is duplex printing. If it is single-sided printing, the process proceeds to S111, and if it is double-sided printing, the process proceeds to S109. In step S111, the control unit 110 feeds the first sheet waiting to be fed using the discharge bin 350 as a discharge destination, and ends the sheet conveyance control. In the case of duplex printing, in step S109, the control unit 110 feeds the first sheet waiting to be fed with the re-feed conveyance path 332 as a discharge destination, and ends the sheet conveyance control. These processes of S109 to S111 are general processes.

  If there is a sheet waiting for refeeding, the process proceeds to S104, and the control unit 110 performs a double-sided circulation interruption determination process and proceeds to S105. Details of the both-side interruption determination process will be described with reference to the flowchart of FIG.

  In step S105, the control unit 110 determines the result of the double-sided circulation interruption determination process in step S104. If the double-sided circulation interruption determination processing is “FALSE”, that is, if it is determined not to be interrupted, the process proceeds to S106, and if not “TRUE” (interrupted), the process proceeds to S107. In S106, the control unit 110 determines whether or not the number of sheets waiting for refeeding is larger than (the double-sided circulation sheet number -1 obtained from the table of FIG. 9) / 2. For example, for a sheet having a paper size “A4” and a paper type “plain paper”, the double-sided circulation number is “5” from FIG. In this case, (5-1) / 2 = 2. In this case, if the number of papers waiting for refeeding is “1” or “2”, the process proceeds from S106 to S109, and if the number of papers waiting for refeeding is “3”, the process proceeds from S106 to S108. In step S108, the control unit 110 re-feeds the paper discharge bin 350 as a paper discharge destination in order to print an image on the back surface of the first paper waiting for re-feeding, and ends the sheet conveyance control. If it is determined in S105 that the process is interrupted, the process proceeds to S107, and the control unit 110 turns on the double-sided circulation interrupt flag on the RAM 150 and proceeds to S108.

  On the other hand, if the double-sided circulation interruption flag is turned on in S101, or if there is no paper waiting to be fed in S102, the process proceeds to S112, and it is determined whether or not there is paper waiting for refeeding. If it is determined that there is a paper waiting for refeeding, the process proceeds to S108. If it is determined that there is no paper waiting for refeeding, the process proceeds to S113, and the control unit 110 turns off the double-sided circulation interruption flag on the RAM 150. Then, the sheet conveyance control is finished.

  With the above processing, as described with reference to FIG. 12, not only the double-sided circulation in paper units but also the conveyance speed of the printing surface is compared to determine whether the double-sided circulation is continued or interrupted. Paper feeding can be controlled.

  FIG. 14 is a flowchart for explaining the determination process of whether or not to interrupt the double-sided circulation in S104 of FIG.

  This process is started when the control unit 110 starts a process for determining whether or not to interrupt the double-sided circulation. First, in step S201, the control unit 110 determines whether the paper waiting to be fed is single-sided printing or double-sided printing. to decide. In the case of single-sided printing, the process advances to step S205, and the control unit 110 sets the double-sided circulation interruption determination to TRUE (interrupts double-sided circulation) and ends this determination process.

  On the other hand, if it is determined in step S201 that double-sided printing is performed, the process advances to step S202, and the control unit 110 obtains the double-sided circulation number by referring to the table in FIG. The process proceeds to S203. In S203, the control unit 110 refers to the table in FIG. 9 based on the paper size and paper type of the last paper waiting to be re-fed, obtains the double-sided circulation number, and proceeds to S204. In step S204, the control unit 110 determines whether or not the double-sided circulation number obtained in steps S202 and S203 matches. If it is determined that there is a mismatch, the process proceeds to S205, where it is determined that the double-sided circulation is interrupted, and the process ends.

  If it is determined in S204 that the values match, the process proceeds to S206, and the control unit 110 obtains the conveyance speed with reference to the table of FIG. 9 based on the paper size, paper type, and resolution of the paper supply surface of the first paper waiting for paper supply. The process proceeds to S207. In step S207, the control unit 110 refers to the table in FIG. 9 based on the paper size, paper type, and resolution of the refeed surface of the first paper waiting for paper supply, determines the transport speed, and proceeds to step S208. In S208 (first determination), the control unit 110 determines whether or not the conveyance speeds obtained in S206 and S207 match. If it is determined that they do not match, the control unit 110 proceeds to S205, determines that double-sided circulation is interrupted, and ends the processing. To do.

  If it is determined in S208 that they match, the process proceeds to S209, and the control unit 110 refers to the table in FIG. 9 based on the paper size, paper type, and resolution of the final paper supply surface waiting for refeeding, and the conveyance speed. To S210. In S210 (second determination), the control unit 110 determines whether or not the transport speeds obtained in S206 and S209 match. If they match, the process proceeds to S211; if they do not match, the process proceeds to S205, where it is determined that the double-sided circulation is interrupted, and the process ends.

  In S211, the control unit 110 refers to the table of FIG. 9 based on the paper size, paper type, and resolution of the refeed surface of the final paper waiting for refeeding, determines the transport speed, and proceeds to S212. In S212 (third determination), the control unit 110 determines whether or not the transport speeds obtained in S206 and S211 match. If the conveyance speeds coincide with each other, the process proceeds to S213, where the determination of interruption of double-sided circulation is determined as FALSE (double-sided circulation is not interrupted), and this process is terminated. On the other hand, if it is determined in S212 that the transport speeds obtained in S206 and S211 do not match, the process proceeds to S205, where it is determined that the double-sided circulation is interrupted, and the process is terminated.

Based on the above determination process, based on the paper size, paper type, and resolution,
(1) Whether or not the process speeds of the first sheet waiting for feeding and the sheet feeding surface coincide with those of the refeeding surface of the first sheet waiting for feeding.
(2) Whether or not the process speeds of the first sheet waiting for sheet feeding and the sheet feeding surface match the sheet feeding surface of the last sheet waiting for refeeding.
(3) Whether the process speeds of the first sheet waiting for sheet feeding and the sheet feeding surface are the same as those of the sheet refeeding surface of the last sheet waiting for refeeding.

  When any of these three does not match, it is determined to interrupt the double-sided circulation.

  Next, a sheet conveyance control method of the image forming apparatus according to the first embodiment will be described with reference to FIGS. 13, 14, 15, and 16.

  FIG. 15 is a diagram illustrating an example of paper (sheet) output by the image forming apparatus according to the first embodiment. Here, there are a total of nine sheets of paper A to paper I, and the single-sided printing and the double-sided printing are performed for only the paper B on the single side and the double side. The paper size is A3 only for paper C and A4 for all the rest. The paper types are all plain paper, and the resolution is 600 dpi for the first to fifth pages of the original, 1200 dpi for the 6th to 14th pages, 600 dpi for the 15th page, and 1200 dpi for the 16th and 17th pages. Here, the printing surface with a resolution of 1200 dpi is shown by shading.

  FIG. 16 is a diagram illustrating the order of sheets fed and re-fed by the image forming apparatus according to the first embodiment.

  First, when feeding the paper A, the control unit 110 proceeds to S101, S102, S103, S110, and S109 in FIG. 13, and discharges the paper A that is the first paper waiting to be fed through the refeed conveyance path 332. Paper is fed as a paper tip, and sheet conveyance control is terminated. Next, when paper B is fed, the process advances to S101, S102, S103, and S104 in FIG. 13 to perform double-sided circulation interruption determination processing.

  In the double-sided circulation interruption process, the process proceeds to S201 in FIG. 14. Since the paper B that is waiting to be fed is single-sided printing, the process proceeds to S205, and the interruption determination of double-sided circulation is determined to be TRUE (interrupt). Thereafter, the process proceeds to S105, S107, and S108 in FIG. 13, and the sheet A, which is the first sheet waiting for refeeding, is fed again using the discharge bin 350 as the discharge destination, and the sheet conveyance control is completed.

  Next, when the paper B is fed again, the control unit 110 proceeds to S101, S102, S103, S110, and S111 in FIG. Paper is fed as a paper discharge destination, and sheet conveyance control is terminated.

  Next, when the paper C is fed, the control unit 110 proceeds to S101, S102, S103, S110, and S109 in FIG. Paper is fed as a paper discharge destination, and sheet conveyance control is terminated.

  Next, when the paper D is fed, the control unit 110 proceeds to S101, S102, S103, and S104 in FIG. 13 and performs a double-sided circulation interruption determination process. In the double-sided circulation interruption process, the process proceeds to S201 in FIG. 14, and since the paper D that is waiting to be fed is double-sided printing, the process proceeds to S202, S203, and S204. Since the size of the paper C is “A3” and the type is “plain paper”, the double-sided circulation number is “3”. Further, since the size of the paper D is “A4” and “plain paper”, the number of both-side circulation is “5”. As a result, in S204, the double-sided circulation number of the paper C and the paper D does not match, so the process proceeds to S205, and the double-sided circulation interruption determination is TRUE. Thereafter, the process proceeds to S105, S107, and S108 in FIG. 13, and the sheet C, which is the first sheet waiting for refeeding, is fed again using the discharge bin 350 as a discharge destination, and the sheet conveyance control is completed.

  Next, when feeding the paper D again, the control unit 110 proceeds to S101, S102, S103, S110, and S109 in FIG. Paper is fed using the paper feed conveyance path 332 as a paper discharge destination, and the sheet conveyance control is terminated. Next, when the paper E is fed, the control unit 110 proceeds to S101, S102, S103, and S104 in FIG. 13 and determines whether to interrupt double-sided circulation. In this determination process, the process proceeds to S201 in FIG. 14, and the process proceeds to S202 because the paper F that is waiting to be fed is duplex printing. Then, the process proceeds to S203 and S204. Here, both the paper D and the paper E are the same for the sizes “A4” and “plain paper”, and in FIG. Further, the process proceeds to S207 and S208, and the conveyance speeds of the paper E feeding surface (the 8th page of the original) and the paper E refeeding side (the 9th page of the original) are compared. The paper E feeding surface and the paper E refeeding surface are both “A4” in size, “plain paper”, and the same resolution as “1200 dpi”. From FIG. 9, the conveyance speed matches “half speed”. The process proceeds to S209. In S209, the paper E feeding surface (the 8th page of the original) and the paper D feeding surface (the 6th page of the original) are both common to “A4”, “plain paper”, and “1200 dpi”, and the transport speed is shown in FIG. In order to become “half speed”, the process proceeds to S211.

  Further, the paper E feeding surface (page 8 of the original document) and the paper D refeeding surface (page 7 of the original document) are both common to “A4”, “plain paper”, and “1200 dpi”, and the conveyance speed is shown in FIG. Since it is “half speed”, the process proceeds from S212 to S213, and the interruption determination of the double-sided circulation is FALSE. Thereafter, the process proceeds to S105, S106, and S109 in FIG. 13, and the sheet E, which is the first sheet waiting to be fed, is fed using the refeed conveyance path 332 as a discharge destination for duplex printing, and the sheet conveyance control is finished. To do.

  Next, when the paper F is fed, the control unit 110 proceeds to S101, S102, S103, and S104 in FIG. In this determination process, the process proceeds to S201 in FIG. 14, and the process proceeds to S202 because the paper F that is waiting to be fed is duplex printing. Then, the process proceeds to S203 and S204. Since both the paper E and the paper F are “A4” and “plain paper”, the double-sided circulation number is “5” from FIG. 9, and the process proceeds to S206. Further, in S207 and S208, the conveyance speeds of the paper F feeding surface (the 10th page of the original) and the refeeding side of the paper F (the 11th page of the original) are compared. Here, the paper F feeding surface and the paper F refeeding surface are both “A4”, “plain paper”, and “1200 dpi”, and the transport speed is “half speed” from FIG. Further, the paper F feeding surface (10th page of the original) and the paper E feeding surface (8th page of the original) are both “A4”, “plain paper”, and “1200 dpi”, and the transport speed is equal to “half speed”. Therefore, the process proceeds to S211.

  Further, the conveyance speeds of the paper F feeding surface (10th page of the original document) and the paper E refeeding surface (9th page of the original document) are compared. Here, the feeding surface of the paper F and the refeeding surface of the paper E are both “A4”, “plain paper”, and “1200 dpi”, and the transport speed is “half speed” from FIG. It is determined not to interrupt. Thereafter, the process proceeds to S105, S106, and S109 in FIG. 13, and the sheet F, which is the first sheet waiting to be fed, is fed using the refeed conveyance path 332 as a discharge destination for duplex printing, and the sheet conveyance control ends. To do.

  Next, when the paper G is fed, the control unit 110 proceeds to S101, S102, S103, and S104 in FIG. 13 and determines whether to interrupt the double-sided circulation. In this process, the process proceeds to S201 in FIG. 14, and the process proceeds to S202 because the paper G that is waiting to be fed is duplex printing. Then, the process proceeds to S203 and S204. Both the paper F and the paper G are “A4” and “plain paper”, and the double-sided circulation sheet number is “5” from FIG. 9, so the process proceeds to S206. Further, the process proceeds to S207 and S208, and the conveyance speeds of the paper G feeding surface (the 12th page of the original document) and the paper G refeeding surface (the 13th page of the original document) are compared. Here, since both the paper G feeding surface and the paper G refeeding surface are “A4”, “plain paper”, and “1200 dpi”, and the transport speed is “half speed”, the process proceeds to S209. Furthermore, the paper G feeding surface (the 12th page of the original) and the paper F feeding surface (the 10th page of the original) are both “A4”, “plain paper”, and “1200 dpi”, and the conveyance speed is “half speed”. Therefore, the process proceeds to S211. In step S212, the conveyance speeds of the paper G feeding surface (the 12th page of the original) and the paper F refeeding surface (the 11th page of the original) are compared. Since both the paper G feeding surface and the paper F refeeding surface are “A4”, “plain paper”, and “1200 dpi”, and the conveyance speed is “half speed”, the process proceeds to S213 so as not to interrupt double-sided circulation. To be determined. Thereafter, the process proceeds to S105 and S106 in FIG. 13, and there are three sheets of paper D, paper E, and paper F that are already waiting for refeeding, which is larger than (two-sided circulation number “5” −1) / 2 = 2. Therefore, the process proceeds to S108, the paper D, which is the first paper waiting for refeeding, is fed again, and the sheet conveyance control is finished.

  Next, when the paper G is fed again, the control unit 110 proceeds to S101, S102, S103, and S104 in FIG. 13 and determines whether to interrupt the double-sided circulation. In this process, the process proceeds to S201 in FIG. 14, and the process proceeds to S202 because the paper G that is waiting to be fed is duplex printing. Then, the process proceeds to S203 and S204. Since both the paper F and the paper G are “A4” and “plain paper” and the double-sided circulation number is “5”, the process proceeds to S206. In S207 and S208, the conveyance speeds of the paper G feeding surface (the 12th page of the original document) and the paper G refeeding surface (the 13th page of the original document) are compared. Here, since both the paper G feeding surface and the paper G refeeding surface are “A4”, “plain paper”, and “1200 dpi” and the transport speed is “half speed”, the process proceeds to S209. Further, the paper G feeding surface (the 12th page of the original) and the paper F feeding surface (the 10th page of the original) are both “A4”, “plain paper”, and “1200 dpi”, and the conveyance speed is “half speed”. Therefore, the process proceeds to S211. In step S212, the conveyance speeds of the paper G feeding surface (the 12th page of the original document) and the paper F refeeding surface (the 11th page of the original document) are compared. Here, both the paper G feeding surface and the paper F refeeding surface are “A4”, “plain paper”, and “1200 dpi”, and the transport speed is “half speed”. judge.

  Thereafter, the process proceeds to S105 and S106 in FIG. In S106, there are two sheets of paper E and paper F that are already waiting to be re-fed, and since it is not greater than (double-sided circulation number “5” −1) / 2 = 2, the process proceeds to S109. In step S109, the first sheet G waiting for sheet feeding is fed using the refeed conveyance path 332 as a sheet discharge destination for both-eye printing, and the sheet conveyance control ends.

  Next, a case where the paper H is fed will be described. The control unit 110 proceeds to S101, S102, S103, and S104 in FIG. 13 and determines whether or not the double-sided circulation is interrupted. In this process, the process proceeds to S201 in FIG. 14, and the process proceeds to S202 because the paper H that is waiting to be fed is duplex printing. The process advances to S203 and S204, and both the paper G and the paper H are “A4” and “plain paper”, and the process advances to S206 in which the double-sided circulation number is “5”. Further, the process proceeds to S207 and S208, where the paper H feeding surface (the 14th page of the original) is “A4”, “plain paper”, “1200 dpi”, and the conveyance speed is “half speed”. On the other hand, the refeeding surface of the paper H (the 15th page of the document) is “A4”, “plain paper”, “600 dpi”, the transport speed is “constant speed”, and the transport speeds do not match. For this reason, it progresses to S205 and it determines with discontinuing double-sided circulation. Thereafter, the process proceeds to S105, S107, and S108 in FIG. 13, and the sheet E, which is the first sheet waiting for refeeding, is fed again with the discharge bin 350 as the discharge destination, and the sheet conveyance control is finished. That is, the double-sided printing of the paper E is not executed continuously.

  Next, it is determined whether the paper H waiting to be fed is fed or the paper F waiting to be fed again is fed again. At this time, the control unit 110 proceeds from S101 to S112 and S108 because the double-sided circulation interruption flag is turned on in S107 when the paper H is determined to be fed. In S108, the sheet F, which is the first sheet waiting for refeeding, is fed again using the discharge bin 350 as the discharge destination, and the sheet conveyance control is completed.

  Next, it is determined whether the paper H waiting to be fed is fed or the paper G waiting for refeeding is fed again. At this time, the control unit 110 proceeds from S101 to S112 and S108 in FIG. 13 because the double-sided circulation interruption flag is turned on in S107 when it is determined to feed the previous paper H. In step S108, the first sheet G waiting for refeeding is re-feeded using the discharge bin 350 as a discharge destination, and the sheet conveyance control is terminated.

  Next, when the paper H is fed, the control unit 110 proceeds from S101 to S112 because the double-sided circulation interruption flag is turned on in S107 when the paper H is judged to be fed. In S112, since the paper F and paper G waiting for refeeding have already been refeeded, there is no paper waiting for refeeding. For this reason, the process proceeds to S113, the duplex interruption flag is turned off, and the process proceeds to S110 and S109, where the first sheet H waiting to be fed is fed with the refeed conveyance path 332 as a delivery destination for duplex printing. Then, the sheet conveyance control is terminated.

  Next, when the paper I is fed, the control unit 110 proceeds to S101, S102, S103, and S104 in FIG. 13 and determines whether or not the double-sided circulation is interrupted. Then, the process proceeds to S203 and S204 in FIG. 14. Since both the paper H and the paper I are “A4” and “plain paper” and the double-sided circulation number is “5”, the process proceeds to S206. Further, the process proceeds to S207 and S208, and the conveyance speeds of the paper I feeding surface (the 16th page of the original) and the paper I refeeding side (the 17th page of the original) are compared. Here, since both the paper I feeding surface and the paper I refeeding surface are “A4”, “plain paper”, and “1200 dpi”, and the transport speed is “half speed”, the process proceeds to S209. The paper I feeding surface (the 16th page of the original) and the paper H feeding surface (the 14th page of the original) are both “A4”, “plain paper”, and “1200 dpi”, and the transport speed is “half speed”. The process proceeds to S211. In step S212, the paper I feed surface (the 16th page of the original) is “A4”, “plain paper”, “1200 dpi”, and the transport speed is “half speed”. On the other hand, the refeed surface of the paper H (the 15th page of the original) is “A4”, “plain paper”, “600 dpi”, and the transport speed is “constant speed”, which is inconsistent. For this reason, it progresses to S205 and it determines with interrupting double-sided circulation. Thereafter, the process proceeds to S105, S107, and S108 in FIG. 13, and the sheet H, which is the first sheet waiting for refeeding, is fed again using the discharge bin 350 as the discharge destination, and the sheet conveyance control is finished.

  Next, when the paper I is fed again, the control unit 110 proceeds to S101, S102, S103, S110, and S109 in FIG. Paper is fed as a paper discharge destination, and sheet conveyance control is terminated. When the paper I is finally re-feeded, the control unit 110 proceeds to S101, S102, S112, and S108 in FIG. 13 and discharges the paper I, which is the first paper waiting for re-feeding, from the paper discharge bin 350. The sheet is fed again as the destination, and this sheet conveyance control is terminated.

  The order of paper feed and refeed as described above is shown in FIG.

  According to the method according to the first embodiment described above, when determining whether to continue double-sided circulation, the resolution of the paper feeding surface of the next paper to be fed (recording medium) and the refeeding surface are different, or Next, it is determined whether or not the resolution of the paper feeding surface of the paper to be fed is different from the resolution of the paper feeding surface of the previous paper fed. Further, it is determined whether the resolution of the paper feeding surface of the next paper to be fed is different from the resolution of the paper refeeding surface of the previous paper fed, and if the resolution is different under any condition, the double-sided circulation is interrupted. By determining, double-sided printing can be performed efficiently.

[Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIG. 17, FIG. 18, and FIG. Note that the configurations of the image forming apparatus (multifunction device) and the image input / output system according to the second embodiment are the same as those of the first embodiment described above, and thus the description thereof is omitted.

  FIG. 17 is a diagram illustrating an example of double-sided imposition in the second embodiment. Specifically, there are 10 pages of the document and the basic resolution is 600 dpi, but only the fourth page of the document has a resolution of 1200 dpi.

  The paper sizes of the papers A to F are all “A4”, and the paper types are all “plain paper”. The resolution is basically 600 dpi, but only the paper C feeding surface (the fourth page of the original) and the refeeding surface (blank paper surface) are 1200 dpi. The 1200 dpi printing surface is shown by shading.

  In FIG. 10 of the first embodiment, the fourth page of the 1200 dpi document is allocated on the back surface of the paper B. However, in the double-sided layout of the second embodiment, the fourth page is allocated on the front surface of the paper C. Also, blank pages with the same resolution as the front surface correspond to the back surfaces of the paper B and the paper C. For this reason, in the double-sided imposition according to the second embodiment, surfaces having different resolutions are not assigned to the front and back sides of the double-sided printing, so that the conveyance speed is not switched between the front and back sides. Therefore, as shown in FIG. 18, the conventional double-sided circulation control in units of paper becomes possible, and the problem of jamming does not occur.

  FIG. 18 is a diagram illustrating the order of sheets fed and re-fed by the image forming apparatus according to the second embodiment.

  FIG. 19 is a flowchart for explaining double-sided layout processing by the control unit 110 of the image forming apparatus according to the second embodiment of the present invention. Note that a program for executing this processing is stored in the ROM 160, developed in the RAM 150, and executed under the control of the CPU 120.

  This process is started when the control unit 110 starts the double-sided imposition process. First, in step S301, the control unit 110 confirms whether a document has been added. If a document to be printed has been added, the process returns to S302. If not, the process returns to S301 to wait for the next document to be added. In step S <b> 302, the control unit 110 determines whether there is a sheet waiting for rear surface imposition. If it is determined that there is a back-side imposition paper, the process proceeds to S303. If not, the process proceeds to S307, and the control unit 110 newly generates a back-side imposition paper, and associates the original with the front surface. The imposition process ends.

  On the other hand, in step S <b> 303, the control unit 110 determines whether the resolution of the document matches the front surface of the paper waiting to be placed on the back side. If it is determined that the resolutions match, the process advances to step S304, and the control unit 110 associates the document with the back side of the paper waiting to be placed on the back side, and then advances to step S305. In step S <b> 306, the control unit 110 performs a paper feed process for paper waiting for back side imposition, and ends this double side imposition process.

  On the other hand, if it is determined that there is a mismatch in S303, the process proceeds to S308, and the control unit 110 associates a blank page with the back side of the paper waiting for back side imposition. In this way, a blank sheet is inserted, and imposition is performed so that the resolutions of the front and back surfaces coincide with each other, and the process proceeds to S309. In step S309, the control unit 110 feeds the back-side imposition paper in which white paper is associated with the back surface in step S308, and the process proceeds to step S307. In step S <b> 307, the control unit 110 newly generates a paper waiting for backside imposition, associates a document with the front side, and ends the double-sided imposition processing.

  As described above, according to the second embodiment, since the resolution of the paper feeding surface of the next paper to be fed (recording medium) and the re-feeding surface always coincide with each other, there is no problem even with double-sided circulation control in units of paper. Can be performed.

(Other examples)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

  110: Control unit, 120: CPU, 130: Image memory, 140: Non-volatile memory, 150: RAM, 160: ROM, 170: Operation unit, 200: Reader unit, 300: Printer unit

Claims (20)

An image forming unit for forming an image on a sheet;
A paper feeder for feeding sheets;
A transport unit that transports a sheet fed from the paper feed unit to the image forming unit, and when the resolution of an image formed by the image forming unit is the first resolution, the sheet is transported at the first transport speed. Is transferred to the image forming unit, and when the resolution of the image formed by the image forming unit is a second resolution higher than the first resolution, the second conveying speed is lower than the first conveying speed. The transport unit for transporting a sheet to the image forming unit;
A double-sided circulation path for reversing the front and back of the sheet that has passed through the image forming unit and refeeding the image forming unit;
The second surface of the sheet that is continuously fed from the sheet feeding unit and forms an image on the first surface of each sheet, and then re-fed to the image forming unit from the duplex circulation path Control means for performing double-sided circulation control that alternately performs a process for forming an image on the sheet and a process for forming an image on the first surface of a sheet newly fed from the sheet feeding unit,
The control means includes
The resolution of the image formed on the first surface of the first sheet conveyed from the sheet feeding unit to the image forming unit, and the sheet is conveyed from the sheet feeding unit to the image forming unit one after the first sheet. The resolution of the image formed on the first surface of the second sheet is the same , and the resolution of the image formed on the second surface of the first sheet is the same as that of the first surface of the second sheet. When the resolutions of the formed images are the same, the double-sided circulation control is continued, and the second sheet is transferred from the sheet feeding unit to the image before forming an image on the second side of the first sheet. Transport to the forming section,
If the resolution of the image formed on the first surface of the first resolution and the second sheet of the image formed on the first side of the sheet are different, or, formed on the second surface of said first sheet If the resolution of the image to be printed differs from the resolution of the image formed on the first surface of the second sheet, the double-sided circulation control is interrupted and the image is formed on the second surface of the first sheet. An image forming apparatus, wherein the second sheet is conveyed from the paper feeding unit to the image forming unit.
An image forming unit for forming an image on a sheet;
  A paper feeder for feeding sheets;
  A transport unit that transports a sheet fed from the paper feed unit to the image forming unit, and when the resolution of an image formed by the image forming unit is the first resolution, the sheet is transported at the first transport speed. Is transferred to the image forming unit, and when the resolution of the image formed by the image forming unit is a second resolution higher than the first resolution, the second conveying speed is lower than the first conveying speed. The transport unit for transporting a sheet to the image forming unit;
  A double-sided circulation path for reversing the front and back of the sheet that has passed through the image forming unit and refeeding the image forming unit;
  The second surface of the sheet that is continuously fed from the sheet feeding unit and forms an image on the first surface of each sheet, and then re-fed to the image forming unit from the duplex circulation path Control means for performing double-sided circulation control that alternately performs a process for forming an image on the sheet and a process for forming an image on the first surface of a sheet newly fed from the sheet feeding unit,
  The control means includes
    The resolution of the image formed on the first surface of the first sheet conveyed from the sheet feeding unit to the image forming unit, and the sheet is conveyed from the sheet feeding unit to the image forming unit one after the first sheet. When the resolution of the image formed on the first surface of the second sheet is the same, the double-sided circulation control is continued and the second image is formed before forming the image on the second surface of the first sheet. Sheet from the sheet feeding unit to the image forming unit,
    When the resolution of the image formed on the first surface of the first sheet is different from the resolution of the image formed on the first surface of the second sheet, the double-sided circulation control is interrupted, and the first An image forming apparatus, comprising: forming an image on a second surface of a sheet; and transporting the second sheet from the paper feeding unit to the image forming unit. An image forming unit for forming an image on a sheet;
  A paper feeder for feeding sheets;
  A transport unit that transports a sheet fed from the paper feed unit to the image forming unit, and when the resolution of an image formed by the image forming unit is the first resolution, the sheet is transported at the first transport speed. Is transferred to the image forming unit, and when the resolution of the image formed by the image forming unit is a second resolution higher than the first resolution, the second conveying speed is lower than the first conveying speed. The transport unit for transporting a sheet to the image forming unit;
  A double-sided circulation path for reversing the front and back of the sheet that has passed through the image forming unit and refeeding the image forming unit;
  The second surface of the sheet that is continuously fed from the sheet feeding unit and forms an image on the first surface of each sheet, and then re-fed to the image forming unit from the duplex circulation path Control means for executing double-sided circulation control that alternately performs a process of forming an image on the sheet and a process of forming an image on the first surface of a sheet newly fed from the paper feeding unit.
  The control means includes
    The resolution of the image formed on the second surface of the first sheet conveyed from the sheet feeding unit to the image forming unit, and the image is conveyed from the sheet feeding unit to the image forming unit one after the first sheet. When the resolution of the image formed on the first surface of the second sheet is the same, the double-sided circulation control is continued and the second image is formed before forming the image on the second surface of the first sheet. Sheet from the sheet feeding unit to the image forming unit,
    When the resolution of the image formed on the second surface of the first sheet is different from the resolution of the image formed on the first surface of the second sheet, the double-sided circulation control is interrupted, and the first sheet An image forming apparatus that transports the second sheet from the sheet feeding unit to the image forming unit after forming an image on the second surface of the image forming unit. An image forming unit for forming an image on a sheet;
  A paper feeder for feeding sheets;
  A transport unit that transports a sheet fed from the paper feed unit to the image forming unit, and when the resolution of an image formed by the image forming unit is the first resolution, the sheet is transported at the first transport speed. Is transferred to the image forming unit, and when the resolution of the image formed by the image forming unit is a second resolution higher than the first resolution, the second conveying speed is lower than the first conveying speed. The transport unit for transporting a sheet to the image forming unit;
  A double-sided circulation path for reversing the front and back of the sheet that has passed through the image forming unit and refeeding the image forming unit;
  A plurality of sheets are continuously fed from the sheet feeding unit, an image is formed on the first surface of each sheet, and then the second sheet of the sheet that is re-fed from the duplex circulation path to the image forming unit. Control means for performing double-sided circulation control for alternately performing processing for forming an image on a surface and processing for forming an image on a first surface of a sheet newly fed from the paper feeding unit,
  The control means includes
    The resolution of the image formed on the first surface of the second sheet conveyed from the paper feeding unit to the image forming unit after the first sheet and the image formed on the second surface of the second sheet When the resolution is the same, the double-sided circulation control is continued, and the second sheet is conveyed from the paper feeding unit to the image forming unit before forming an image on the second surface of the first sheet. Let
    When the resolution of the image formed on the first surface of the second sheet is different from the resolution of the image formed on the second surface of the second sheet, the double-sided circulation control is interrupted, and the first An image forming apparatus, comprising: forming an image on a second surface of a sheet; and transporting the second sheet from the paper feeding unit to the image forming unit. An image forming unit for forming an image on a sheet;
A paper feeder for feeding sheets;
A transport unit that transports a sheet fed from the paper feed unit to the image forming unit, and when the resolution of an image formed by the image forming unit is the first resolution, the sheet is transported at the first transport speed. Is transferred to the image forming unit, and when the resolution of the image formed by the image forming unit is a second resolution higher than the first resolution, the second conveying speed is lower than the first conveying speed. The transport unit for transporting a sheet to the image forming unit;
A double-sided circulation path for reversing the front and back of the sheet that has passed through the image forming unit and refeeding the image forming unit;
A plurality of sheets having the same paper size and paper type are continuously fed from the paper feed unit to form an image on the first surface of each sheet, and then re-transferred from the double-sided circulation path to the image forming unit. Double-sided circulation control is performed in which an image forming process on the second surface of the fed sheet and an image forming process on the first surface of the newly fed sheet from the sheet feeding unit are alternately performed. Control means, and
The control means includes
The resolution of the image formed on the first surface of the second sheet conveyed from the paper feeding unit to the image forming unit after the first sheet is the resolution of the image formed on the first surface of the first sheet . And the resolution of the image formed on the second surface of the first sheet is the same, and the resolution of the image formed on the first surface of the second sheet is the same as that of the second sheet. Again the resolution of the image formed on the second surface are the same, continuing the double-sided circulation control, the paper said second sheet before forming the image on the second surface of said first sheet Conveyed from the paper section to the image forming section,
The resolution of the image formed on the first surface of the second sheet is different from the resolution of the image formed on the first surface or the second surface of the first sheet, or of the second sheet If the resolution of the image formed on the first surface is different from the resolution of the image formed on the second surface of the second sheet, the double-sided circulation control is interrupted, and the second surface of the first sheet is An image forming apparatus that transports the second sheet from the paper feeding unit to the image forming unit after forming an image.
The image forming unit includes:
A photosensitive drum;
Polygon mirror,
A laser emission unit that irradiates the photosensitive drum with laser light according to image data through the polygon mirror, and forms an image on the photosensitive drum;
A transfer portion for transferring an image on the photosensitive drum to a sheet;
The image forming apparatus according to any one of claims 1 to 5, characterized in that it has a. The image forming apparatus according to claim 6 , wherein the rotation speed of the polygon mirror at the second resolution is the same as the rotation speed of the polygon mirror at the first resolution. The image forming apparatus according to claim 6, wherein the first and second conveyance speeds are sheet conveyance speeds when passing through the transfer unit. The first resolution is 600 dpi, the image forming apparatus according to any one of claims 1 to 8, wherein the second resolution is 1200 dpi. Said second conveying speed, the image forming apparatus according to any one of claims 1 to 9, characterized in that said first one-half of the transport speed. The first sheet, the image forming apparatus according to any one of claims 1 to 10, characterized in that the last sheet of the sheet already fed from the paper feeding unit. The second sheet, the image forming apparatus according to any one of claims 1 to 11, characterized in that a first sheet of the sheets fed from the paper feeding unit. When the control unit interrupts the double-sided circulation control , the control unit discharges all the sheets staying in the apparatus including the first sheet from the image forming apparatus , and then removes the second sheet from the image forming unit. the image forming apparatus according to any one of claims 1 to 10, characterized in that to convey to. The control means compares the resolution of an image after feeding the first sheet from the sheet feeding unit and before feeding the second sheet. The image forming apparatus according to any one of 1 to 11 . In the double-sided circulation control, an image forming apparatus according to any one of claims 1 to 14 and determining the imaging order and feeding order based on circulating sheet number. The image forming apparatus according to any one of claims 1 to 13, wherein the paper type of the second sheet and the first sheet are the same. The image forming apparatus according to any one of claims 1 to 16, wherein the paper size of the first sheet and the second sheet are the same. The first surface is a surface of a sheet to perform duplex printing, the image forming apparatus according to any one of claims 1 to 17, wherein the second surface, characterized in that a back surface of the sheet to perform duplex printing . A receiver for receiving image data;
The image forming unit, an image forming apparatus according to any one of claims 1 to 18 and forming an image on a sheet based on the image data received by the receiving unit.   In the single-sided printing mode, the control unit causes the sheet to be discharged without passing through the double-sided circulation path after forming an image on the first surface of the sheet fed from the paper feeding unit. The image forming apparatus according to claim 1, wherein:

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