JP2019064793A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus for improving double-sided productivity for a paper having a long length in a transporting direction without increasing the length of the double-sided transport path. According to the present invention, a first reversing means for reversing the transport direction of a recording material and transporting the recording material to a first double-sided transport path, and discharging the recording material to the outside or transporting the recording material. An image is formed on both sides of a plurality of recording materials in succession with a second reversing means for reversing the direction and transporting the recording material to a second double-sided transport path that joins in the middle of the first double-sided transport path. When doing so, the first recording material is transported to the second transport path by the guide means, the second recording material is transported to the third transport path by the guide means, and the first reversing means is used to transport the second recording material to the third transport path. Before transporting the first recording material to the first double-sided transport path, the second recording material is transferred to the first double-sided transport path via the second double-sided transport path by the second reversing means. It is characterized by having a control means for controlling the transportation. [Selection diagram] Fig. 6

Description

  The present invention relates to an image forming apparatus capable of forming an image on both sides of a sheet.

  Conventionally, in an image forming apparatus such as a copying machine or a printer, there is one which automatically forms an image on a first side (front side) and a second side (back side) of a sheet. In particular, many small-sized image forming apparatuses adopt the “normal circulation method” in which the first side of a sheet is printed and then the sheet is reversed by a reversing mechanism to print the second side of the sheet. On the other hand, in the case of an image forming apparatus of medium size machine or more, in order to improve double-sided productivity, many adopt an "alternate circulation method" in which the first and second sides of different sheets are printed alternately. In the alternate circulation method, an image is formed on the first side, and a sheet reversely conveyed and a sheet newly fed from a sheet feeding port are alternately and continuously printed.

  The image forming apparatus of Patent Document 1 is provided with a plurality of double-sided conveyance paths having different lengths, and switches the double-sided conveyance paths to be used according to the length of the sheet. For example, when the length of the sheet to be conveyed is short, a double-sided conveyance path with a short path length is used, and when the length of the conveyed sheet is long, a double-sided conveyance path with a long path length is used. As a result, by conveying a short sheet of paper to the long-side conveyance path having a long path length, it is possible to prevent the conveyance of the sheet from taking time and reducing the both-side productivity.

JP, 2016-118773, A

  Here, in order to realize the alternate circulation method, in order to make the sheet on which the first side is printed stand by, a double-sided conveyance path having a path length longer than the length of the sheet is required. That is, the size of the device is increased. On the other hand, when the length of the double-sided conveyance path is shortened, it is necessary to perform double-sided printing not by the alternate circulation method but by the normal circulation method.

  An object of the present invention is to provide an image forming apparatus which improves double-sided productivity for a sheet having a long length in the conveyance direction without increasing the length of the double-sided conveyance path.

  An image forming apparatus according to the present invention for achieving the above object comprises: feeding means for feeding a recording material from a mounting portion on which the recording material is placed to the first conveyance path; and feeding from the feeding means An image forming unit for forming an image on the recorded recording material; and a second conveyance passage branched from the first conveyance passage or a recording material on which the image is formed by the image formation means is branched from the first conveyance passage Guiding means for guiding to any of the three conveyance paths; first reversing means for inverting the conveyance direction of the recording material conveyed from the second conveyance path; and conveying the recording material to the first double-sided conveyance path And discharging the recording material conveyed from the third conveyance path to the outside, or reversing the conveyance direction of the recording material conveyed from the third conveyance path, and merging in the middle of the first double-sided conveyance path Second reversing means for transporting the recording material to the two-sided transport path of 2; Conveying means for conveying the recording material conveyed to the first both-side conveyance path by the rolling means or the second reversing means again to the first conveyance path, and forming an image on both sides of a plurality of recording materials in succession The first recording material is conveyed to the second conveyance path by the guiding means, and the second recording material following the first recording material is conveyed to the third conveyance path by the guiding means. Before the first recording material is conveyed to the first duplex conveyance path by the first reversing means, the second recording material is conveyed along the second duplex conveyance path by the second reversing means. And control means for performing control so that the sheet is conveyed to the first double-sided conveyance path.

  According to the present invention, it is possible to provide an image forming apparatus capable of improving double-sided productivity for a sheet having a long length in the conveyance direction without increasing the length of the double-sided conveyance path.

Overall configuration of the image forming apparatus Control block diagram showing system configuration of image forming apparatus Flowchart of double-sided conveyance control unit according to the first embodiment Explanatory drawing which shows the operation | movement at the time of double-sided printing based on Example 1 Explanatory drawing which shows the image formation order in the image formation control part based on Example 1 Flowchart of double-sided conveyance control unit according to the second embodiment Explanatory drawing which shows conveyance path length L1 which concerns on Example 2. Explanatory drawing which shows the image formation order in the image formation control part which concerns on Example 2. Flowchart of double-sided conveyance control unit according to the third embodiment Explanatory drawing which shows conveyance path length L2 which concerns on Example 3. Explanatory drawing which shows the image formation order in the image formation control part based on Example 3

Example 1
<Image forming apparatus>
The general configuration of the image forming apparatus according to the present embodiment will be outlined with reference to FIG. In this embodiment, an electrophotographic laser beam printer 100 (hereinafter referred to as the printer 100) is shown as an image forming apparatus. In FIG. 1, a printer 100 forms an electrostatic latent image by image light formed based on pixel signals transmitted from a controller unit (not shown), develops this electrostatic latent image, and transfers a visible image by superposition. To form a color visible image. Then, the color visible image is transferred to the sheet 2 and the color visible image on the sheet 2 is fixed. The image forming unit includes a photosensitive drum (5Y, 5M, 5C, 5K), a charging unit (7Y, 7M, 7C, 7K), a developing unit (8Y, 8M, 8C, 8K), and a primary unit. It is configured to include transfer rollers (4Y, 4M, 4C, 4K). Here, the photosensitive drums (5Y, 5M, 5C, 5K), charging units (7Y, 7M, 7C, 7K), and developing units (8Y, 8M, 8C, 8K) are cartridges (22Y, 22M, 22C, and 22K).

  The photosensitive drums (5Y, 5M, 5C, 5K) are formed by applying an organic photoconductive layer on the outer periphery of an aluminum cylinder, and the driving force of a driving motor (not shown) is transmitted to rotate the image forming operation. It rotates clockwise according to it. Each station is provided with four charging units (7Y, 7M, 7C, 7K) for charging photosensitive drums of yellow (Y), magenta (M), cyan (C), and black (K). Each charging unit is provided with charging rollers (7YR, 7MR, 7CR, 7KR). The charging rollers (7YR, 7MR, 7CR, 7KR) uniformly charge the surfaces of the photosensitive drums (5Y, 5M, 5C, 5K). Then, light is selectively emitted from the scanner unit 10 to the surfaces of the photosensitive drums (5Y, 5M, 5C, 5K) to form electrostatic latent images on the photosensitive drums (5Y, 5M, 5C, 5K). Ru. Four development units (8Y, 8M, 8C, 8K) that develop yellow (Y), magenta (M), cyan (C) and black (K) at each station to visualize electrostatic latent images Is provided. Each developing unit is provided with a developing roller (8YR, 8MR, 8CR, 8KR). The developing rollers (8YR, 8MR, 8CR, 8KR) visualize the electrostatic latent images formed on the photosensitive drums (5Y, 5M, 5C, 5K) with toner.

  At the time of image formation, the intermediate transfer belt 12 rotates in the counterclockwise direction in FIG. 1 while being in contact with the photosensitive drums (5Y, 5M, 5C, 5K). The visible images formed on the photosensitive drums (5Y, 5M, 5C, 5K) are primarily transferred onto the intermediate transfer belt 12 by the primary transfer bias applied to the primary transfer rollers (4Y, 4M, 4C, 4K). At the nip portion (secondary transfer position) formed by the secondary transfer roller 9 and the intermediate transfer belt 12, the color visible image formed on the intermediate transfer belt 12 is secondarily transferred to the sheet 2. The primary transfer rollers (4Y, 4M, 4C, 4K) and the secondary transfer roller 9 rotate as the intermediate transfer belt 12 rotates.

  A portion of the visible image is not transferred to the sheet 2 at the secondary transfer position and remains on the intermediate transfer belt 12. Since the visible image remaining on the belt is unnecessary, it is removed by the cleaning operation. In the cleaning operation, the visible image which has become unnecessary is conveyed to the cleaning blade 12 a by the intermediate transfer belt 12, scraped off by the cleaning blade 12 a, and recovered by the waste toner container 12 b to remove the visible image.

  The cassette tray 101 is a placement unit on which a plurality of sheets 2 (recording materials) are placed. The sheet feeding roller 102 is rotated by the suction of a sheet feeding solenoid (not shown) while the sheet feeding motor (not shown) is rotating. The sheet feed roller 102 feeds the sheet 2 from the cassette tray 101 to the conveyance path 25. The sheet 2 fed by the sheet feed roller 102 is conveyed to a registration roller 3 (hereinafter referred to as a registration roller 3). A registration sensor 16 (hereinafter referred to as a registration sensor 16) is disposed in the conveyance path 25, and the registration roller 3 conveys the sheet 2 to the secondary transfer position according to the timing when the registration sensor 16 detects the leading edge of the sheet 2. Do.

  The fixing unit 13 fixes the transferred color visible image while conveying the sheet 2 and includes a fixing roller 14 for heating the sheet 2 and a pressure roller 15 for pressing the sheet 2 against the fixing roller 14. Is equipped. The fixing roller 14 and the pressure roller 15 are hollow, and a heater is incorporated in the fixing roller 14. That is, the sheet 2 holding the color visible image is transported by the fixing roller 14 and the pressure roller 15, and heat and pressure are applied to fix the toner on the surface. The sheet 2 on which the visible image is fixed is discharged to the discharge tray 27, and the image forming operation is completed. A fixing discharge sensor 17 is disposed downstream of the fixing unit 13, and detects the presence or absence of the sheet 2 in the conveyance path 25.

  In addition, the printer 100 is provided with a configuration for reversing and conveying the sheet 2 so that an image can be formed on the second surface of the sheet 2 on which the image formation of the first surface is completed. In the present embodiment, the first reverse roller 62 that rotates in the forward and reverse direction in response to the driving force from the first reverse motor 220 whose operation is controlled by the double-sided conveyance control unit 207 shown in FIG. 2 is provided. The forward rotation of the first reverse roller 62 pulls in the sheet 2 fed from the conveyance path 60, and the reverse direction of the first reverse roller 62 reverses the conveyance direction of the pulled-in sheet 2, Is conveyed to the double-sided conveyance path 56. The transport path 60 is one of the transport paths branched from the transport path 25.

  In addition, the printer 100 is provided with a second reverse discharge roller 52 that receives forward and reverse rotation in response to the driving force from the second reverse discharge motor 221 whose operation is controlled by the duplex conveyance control unit 207. When the second reverse sheet discharge roller 52 rotates forward, the sheet 2 fed from the conveyance path 63 is drawn in, and the sheet 2 is discharged to the outside of the printer 100. Then, when the second reverse sheet ejection roller 52 reversely rotates, the conveyance direction of the drawn-in sheet 2 is reversed, and the sheet 2 is conveyed to the duplex conveyance path 54. The transport path 63 is one of the transport paths branched from the transport path 25. Here, since the second reverse sheet discharge roller 52 doubles as a reverse roller and a discharge roller, downsizing of the apparatus main body can be realized as compared with the case where the independent rollers are individually held.

  The printer 100 further includes a duplex conveying roller 55 and a duplex refeeding roller 57 that rotate in response to the driving force from the duplex conveying motor 222 whose operation is controlled by the duplex conveying control unit 207. The duplex conveying roller 55 and the duplex refeeding roller 57 transport the sheet 2 reversely transported from the first reversing roller 62 or the second reverse sheet discharging roller 52 to the transporting path 25 along the duplex transporting path 56. Thus, the double-sided conveyance path 56 is configured to merge in the middle of the conveyance path 25.

  The printer 100 also has a double-sided flapper 51 that guides the sheet 2 that has been guided by the conveyance path 25 and has passed through the fixing unit 13 to either the first reverse roller 62 or the second reverse sheet discharge roller 52. . The double-sided flapper 51 can be switched in position by operating the plunger type double-sided flapper solenoid 223 by the double-sided conveyance control unit 207 shown in FIG. 2, and either the first reverse roller 62 or the second reverse sheet discharge roller 52. Guide the sheet 2. In the present embodiment, the double-sided flapper 51 guides the sheet 2 having passed through the fixing unit 13 to the first reverse roller 62 when the double-sided flapper solenoid 223 is pulled (ON). The double-sided flapper 51 guides the sheet 2 to the second reverse sheet discharge roller 52 in a state where the double-sided flapper solenoid 223 is not pulled (OFF).

  Further, the sheet 2 guided to the conveyance path 60 is conveyed by the rotating fixing roller 14 and the pressure roller 15, and reaches the first switching flapper 61 stopped at the position shown by the solid line by its own weight. When the sheet 2 is further conveyed, the sheet 2 reaches the first reversing roller 62 while pushing up the first switching flapper 61, and the leading end of the sheet 2 protrudes from the printer 100 to the outside. Here, until the rear end of the sheet 2 passes the first switching flapper 61 and the rear end of the sheet 2 reaches the both-side reverse position before the first reverse roller 62 by a predetermined distance, 1) The switching flapper 61 returns to the position shown by the solid line in FIG. 1 by its own weight. As a result, when the first reverse roller 62 reversely rotates, the sheet 2 is conveyed along the upper surface of the first switching flapper 61 to the duplex conveying path 56.

  Further, the sheet 2 guided to the conveyance path 63 is conveyed by the rotating fixing roller 14 and the pressure roller 15, and reaches the second switching flapper 53 stopped at the position shown by the solid line by its own weight. When the sheet 2 is further conveyed, the sheet 2 is discharged to the sheet discharge tray 27 while pushing up the second switching flapper 53. However, when the sheet 2 on which the image is formed is conveyed on the first side of the double-sided job, the reverse operation described below is performed. The sheet 2 reaches the second reverse sheet discharging roller 52 while pushing up the second switching flapper 53, and the leading end of the sheet 2 protrudes from the printer 100 to the outside. Here, by the time the rear end of the sheet 2 passes the second switching flapper 53 and the rear end of the sheet 2 reaches the both-sides reverse position before the second reverse discharge roller 52 by a predetermined distance. The second switching flapper 53 returns to the position shown by the solid line in FIG. 1 by its own weight. As a result, when the second reverse sheet ejection roller 52 reversely rotates, the sheet 2 passes along the upper surface of the second switching flapper 53 through the duplex conveying path 54 and merges into the middle of the duplex conveying path 56 and is transported.

<Control Unit Configuration of Image Forming Apparatus>
Next, the system configuration of the entire control unit of the printer 100 will be described using the block diagram of FIG. In FIG. 2, 206 is a host computer, 205 is a controller, and 201 is an engine control unit. The engine control unit 201 further includes a sheet conveyance control unit 203, a double-sided conveyance control unit 207, and an image formation control unit 204.

  The controller 205 receives a print command from the host computer 206, and sends a print command including whether or not it is a single-sided or double-sided print job based on the received information to the engine control unit 201. Based on a print command from the controller 205, the engine control unit 201 instructs the various types of actuators from the sheet conveyance control unit 203, the double-sided conveyance control unit 207, and the image formation control unit 204.

  The sheet conveyance control unit 203 rotates the sheet feeding motor 210 at the start of feeding, and causes the sheet feeding roller 102 to rotate by suctioning the sheet feeding solenoid 211. Thus, the sheet 2 is fed from the cassette tray 101 to the conveyance path 25. The fed sheet 2 is further conveyed to the secondary transfer roller 9 by the registration roller 3. At this time, the arrival timing of the leading edge and the trailing edge of the sheet 2 can be detected by the registration sensor 16, so the sheet conveyance control unit 203 determines the occurrence of jamming, the length in the sheet 2 conveyance direction, and the feeding operation is completed. Can be judged.

  The double-sided conveyance control unit 207 switches the position of the double-sided flapper 51 by operating the double-sided flapper solenoid 223 and guides the sheet 2 to one of the first reverse roller 62 and the second reverse paper discharge roller 52. The determination of switching in this embodiment will be described later. The double-sided conveyance control unit 207 causes the first reverse motor 220 to rotate in the forward and reverse direction with respect to the sheet 2 guided by the first reverse roller 62 to drive the first reverse roller 62, and the sheet from the conveyance path 60 to the double-sided conveyance path 56 Transport 2 At this time, the duplex conveyance control unit 207 detects the rear end of the sheet 2 by the fixing discharge sensor 17 and stops the forward rotation driving of the first reversing motor 220 based on the detected timing. Further, for the sheet guided by the second reverse sheet discharge roller 52 and discharged to the sheet discharge tray 27, the second reverse sheet discharge motor 221 rotates forward and discharges it to the outside of the machine. For the sheet 2 guided by the second reverse discharge roller 52 and not discharged to the discharge tray 27, the second reverse discharge motor 221 is rotated forward and reverse to drive the second reverse discharge roller 52. The sheet 2 is conveyed to the duplex conveyance path 54. At this time, the duplex conveyance control unit 207 detects the rear end of the sheet 2 by the fixing and discharging sensor 17 and stops the forward rotation driving of the second reverse sheet discharging motor 221 based on the detected timing.

  The image formation control unit 204 controls the order and timing of forming an image. The image forming control unit 204 forms an image on the image forming unit in the image forming order shown in FIG. 5A when performing the normal circulation double-sided printing. FIG. 5A shows the relationship between the image formation order and time. In the figure, for example, “1-2” represents “the second side of the first sheet”, and “2-1” represents the “first side of the second sheet”. The relationship between the image formation order and time in this embodiment will be described later.

<Double-sided conveyance control>
Next, double-sided conveyance control performed by the double-sided conveyance control unit 207, which is a feature of the present embodiment, will be described using FIGS. 3 and 4. FIG.

  Whether the duplex conveying control unit 207 of the present embodiment operates the duplex flapper solenoid 223 according to the determination shown in the flowchart of FIG. 3 and guides the sheet 2 to either the first reverse roller 62 or the second reverse sheet discharge roller 52 To judge. Upon receiving the print command from the controller 205, the double-sided conveyance control unit 207 determines whether the print command is a double-sided job (S601). Then, when the print job is a single-sided print job, the duplex conveyance control unit 207 guides the sheet 2 to the second reverse sheet ejection roller 52 (S602). If the print job is a double-sided job, the double-sided conveyance control unit 207 determines whether the sheet 2 fed next from the cassette tray 101 is an odd-numbered sheet (for example, the first sheet, the third sheet, etc.). (S603). If the sheet 2 fed from the cassette tray 101 is an even-numbered sheet (for example, the second sheet, the fourth sheet, etc.), the duplex conveyance control unit 207 guides the sheet 2 to the second reverse sheet discharge roller 52 and reverses the sheet. The transportation is performed (S604). If the sheet 2 fed from the cassette tray 101 is an odd-numbered sheet, the duplex conveyance control unit 207 determines whether the sheet 2 fed from the cassette tray 101 is a sheet to be fed at the end of the job. (S605). If the sheet 2 to be fed from the cassette tray 101 is a sheet to be fed at the end of the job, the duplex conveyance control unit 207 guides the sheet 2 to the second reverse sheet discharge roller 52 to perform the reverse (S604). If the sheet 2 fed from the cassette tray 101 is not the sheet to be fed at the end of the job, the duplex conveyance control unit 207 guides the sheet 2 to the first reversing roller 62 and carries out reverse conveyance (S606).

  Here, since the path length from the duplex reversing to the merging into the conveyance path 25 is shorter when the second reverse sheet discharging roller 52 is used compared to the first reverse roller 62, the sheet is fed at the end of the double-sided job in S605. The method for guiding the sheet to be fed to the second reverse discharge roller 52 has been described. However, in order to simplify double-sided conveyance control executed by the double-sided conveyance control unit 207, whether it is the odd-numbered sheet whether or not it is the last sheet to be fed in the double-sided job (S603) A method of switching the first reverse roller 62 and the second reverse sheet discharge roller 52 may be applied.

  Further, in the present embodiment, the method of determining whether or not the sheet 2 fed from the cassette tray 101 is the odd-numbered sheet when the print command from the controller 205 is received (S603) has been described. However, instead of receiving a print command from the controller 205, it may be determined when the sheet conveyance control unit 203 starts feeding of the sheet 2 or when the image formation control unit 204 starts image formation. It is also possible to determine whether the double-sided conveyance control unit 207 controls reverse conveyance using the first reverse roller 62 instead of the order of the sheets 2 to be fed. As a result, even if double-sided printing of the normal circulation method is mixed in the same double-sided job, improvement in double-sided productivity can be realized.

  Next, the double-sided conveyance control sequence of this embodiment executed by the sheet conveyance control unit 203 and the double-sided conveyance control unit 207 will be specifically described with reference to FIG. Here, FIG. 4 corresponds to the configuration of the printer 100 shown in FIG.

  For example, when duplex printing is performed on two sheets having a length in the transport direction in which duplex printing can not be performed by the alternate circulation method using the first reversing roller 62, the printer 100 feeds the first sheet 701 first. The first side of the first sheet of paper 701 is printed (FIG. 4A). In parallel with the conveyance of the first sheet of paper 701 to the first reverse roller 62, the printer 100 subsequently feeds the second sheet of paper 702, and the first side of the second sheet of paper 702 is fed. Is printed second (FIG. 4 (b)). Thereafter, the printer 100 causes the sheet 701 to stop and stand by at the timing when the trailing edge of the first sheet of the fed sheet 701 reaches the predetermined distance of the first reverse roller 62 before. The printer 100 conveys the fed second sheet 702 to the second reverse discharge roller 52 (FIG. 4C). Next, the printer 100 reversely conveys the fed second sheet 702 earlier than the fed first sheet 701 (FIG. 4 (d)). Thereafter, in parallel with the fact that the second side of the fed second sheet of paper 702 which has passed through the duplex conveying path 56 is printed third, the printer 100 continues to feed the first sheet of the fed second sheet 702. The sheet of paper 701 is conveyed reversely. The printer 100 prints the second side of the first fed sheet 701 fourth (FIG. 4E). Then, the printer 100 conveys the sheet 702 and the sheet 701 to the second reverse sheet discharging roller 52 in the order of the second sheet of the fed sheet 702 and the first sheet of the fed sheet 701 in the order in which the second side was printed. Discharge to the outside (Fig. 4 (f)).

  Here, in FIG. 4D, the reason why the second sheet of the fed sheet 702 is reversed and conveyed earlier than the first sheet of the sheet 701 will be described. In the present embodiment, the second reverse sheet discharging roller 52 plays not only the role of reversing means for reversing the conveyance direction of the sheet 2 but also plays the role of discharging means for discharging the sheet 2 to the outside of the printer 100. Therefore, even if the first fed sheet 701 is reversed first, the second fed sheet 702 is present at the position of the second reverse sheet discharge roller 52, and the sheet 701 is transferred to the outside of the printer 100. It is because it can not be discharged.

<Image formation control>
Next, image formation control performed by the image formation control unit 204, which is a feature of the present embodiment, will be described with reference to FIG.

  5 (a) and 5 (b) show the case of executing two double-sided jobs, and FIG. 5 (a) shows the case of performing double-sided printing by the normal circulation method as a comparison, FIG. 5 (b) Shows the case of performing double-sided printing in the present embodiment. 5 (a) and 5 (b) show the relationship between the image formation order and time. As described above, for example, “1-2” represents “the second surface of the first sheet”, and “2-1” represents the “first surface of the second sheet” in the drawing. Further, “(first reverse)” in the drawing represents an image on the sheet conveyed to the first reverse roller 62, and “(second reverse)” represents an image on the sheet conveyed to the second reverse sheet discharge roller 52. , “(Discharge)” indicates that the image is for a sheet discharged to the discharge tray 27.

  In double-sided printing by the normal circulation method, which is a comparative example, after printing the first side of the sheet, it is reversed by the second reverse sheet discharging roller 52 and passes halfway through the double-sided conveying path 54 and the double-sided conveying path 56 to the conveying path 25 It takes time to transport. Therefore, it is necessary to widen the image interval between the first surface and the second surface ("image interval A" in FIG. 5A).

  On the other hand, in the present embodiment, as described with reference to FIG. 4, the sheet to be fed first is conveyed to the first reverse roller 62, and the sheet to be fed second is subsequently subjected to the second reverse discharge. It is conveyed by the roller 52. That is, the image formation can be performed without the need to widen the image interval between the image “2-1” for the sheet fed first and the image “1-1” for the sheet fed second (FIG. 5 (b)). Inside "image interval B"). After that, the images “1-1” and “1-2” for the second fed sheet are reversed by the second reverse sheet discharge roller 52 in the same manner as in the normal circulation system. It takes time to transport to the transport path 25 via the middle. Therefore, it is necessary to widen the image interval between the first surface and the second surface ("image interval A" in FIG. 5 (b)). Finally, since the image interval for the sheet “1-2” which is fed secondly and discharged to the outside of the machine and the sheet “2-2” which is subsequently discharged out of the machine can be transported on both sides continuously, There is no need to extend the image spacing. As a result, in the present embodiment, double-sided productivity can be enhanced by the image interval "A-B" for a sheet having a long length in the transport direction in which double-sided printing can not be performed by the alternate circulation method.

  As described above, in this embodiment, in order to discharge the sheet to be fed secondly prior to the sheet to be fed first, the image forming control unit 204 sets “2-1”, “1”. It is necessary to perform image formation in the order of "1", "1-2" and "2-2". The image formation control unit 204 changes the order of the sheets reversely conveyed by the double-sided conveyance control unit 207 with respect to the controller 205 via the engine control unit 201 at the timing before the image formation on the sheet to be fed first starts. Send a command to notify As a result, the image forming order is switched so that the image formation of “2-1” is performed earlier than “1-1” and “1-2”.

  As described above, according to the embodiment of the present invention, the reversing means is switched so that the sheet to be fed secondly before the sheet to be fed first is discharged to the outside of the machine, and the image forming order Have replaced. As a result, the productivity at the time of double-sided printing on a sheet having a long length in the transport direction can be improved. In addition, since it is not necessary to secure a transport path in which a sheet having a long length in the transport direction can adopt the alternate circulation system, it is possible to realize improvement in duplex productivity while realizing downsizing of the apparatus.

  Further, in the above embodiment, although two double-sided jobs have been described, it is also possible to carry out two or more double-sided jobs. That is, in the case of an even-numbered double-sided job, it is possible to apply by repeating the printing operation of this embodiment. In the case of an odd-numbered double-sided job, the printing operation of the present embodiment is repeatedly performed except for the last fed sheet, and the printing operation similar to the normal circulation type is performed for the last fed sheet. It is applicable.

  In the above embodiment, the case has been described where the first and second sheets are used as one set to perform duplex printing. However, it is not limited to this. For example, the first sheet is conveyed toward the first reverse roller 62, and the second sheet is conveyed toward the second reverse sheet discharge roller 52. Thereafter, the second sheet of paper is reversed, passed through the duplex conveying path 56, and then discharged to the outside by the second reverse paper discharge roller 52. Thereafter, while the first sheet is on standby, the second reverse sheet discharge roller 52 may execute duplex printing on the third and subsequent sheets in a normal circulation system. Then, following the conveyance of the n-th (n ≧ 3) sheet to the duplex conveying path 56, the first sheet, which is on standby, is also transported to the duplex conveying path 56. That is, the set of sheets to which the present invention is applied may not necessarily be the first and second sheets.

Example 2
In this embodiment, control for further optimizing the control of the first embodiment according to the number of double-sided jobs and the length in the sheet conveyance direction will be described. The description of the same parts as in the first embodiment will be omitted.

<Double-sided conveyance control>
Double-sided conveyance control performed by the double-sided conveyance control unit 207, which is a feature of the present embodiment, will be described with reference to FIGS.

  Whether the duplex conveying control unit 207 of the present embodiment operates the duplex flapper solenoid 223 according to the determination shown in the flowchart of FIG. 6 to guide the sheet 2 to either the first reversing roller 62 or the second reversing paper discharge roller 52 To judge. Upon receiving the print command from the controller 205, the double-sided conveyance control unit 207 determines whether the print command is a double-sided job (S801). Then, when the print job is a single-sided print job, the duplex conveying control unit 207 guides the sheet 2 to the second reverse sheet ejection roller 52 (S802). If the print job is a double-sided job, the double-sided conveyance control unit 207 next determines whether the number of jobs is three or more (S803). When the number of jobs is less than three, the double-sided conveyance control unit 207 causes the sheet 2 fed from the cassette tray 101 to be an odd-numbered sheet (for example, the first sheet, the third sheet, etc.) as in the first embodiment. It is determined whether or not (S804). If the sheet 2 fed from the cassette tray 101 is an even-numbered sheet (for example, the second sheet, the fourth sheet, etc.), the duplex conveyance control unit 207 guides the sheet 2 to the second reverse sheet discharge roller 52 and reverses the sheet. The transportation is performed (S805). If the sheet 2 fed from the cassette tray 101 is an odd-numbered sheet, the duplex conveyance control unit 207 determines whether the sheet 2 fed from the cassette tray 101 is a sheet to be fed at the end of the job. (S806). If the sheet 2 to be fed from the cassette tray 101 is a sheet to be fed at the end of the job, the duplex conveyance control unit 207 guides the sheet 2 to the second reverse sheet discharge roller 52 to perform the reverse (S805). If the sheet to be fed from the cassette tray 101 is not the sheet to be fed last, the duplex conveyance control unit 207 guides the sheet 2 to the first reversing roller 62 and performs reverse conveyance (S807).

  On the other hand, when the number of jobs is three or more, the duplex conveyance control unit 207 next determines whether the length L of the sheet 2 in the conveyance direction is shorter than the conveyance path length L1 shown in FIG. 7 (S808). The conveyance path length L1 shown in FIG. 7 is the path length of the double-sided conveyance path 56 from the first reverse roller 62 to the position where the conveyance path 25 merges. That is, it is determined whether or not the length in the transport direction of the sheet 2 is a length that can adopt the alternate circulation method. In the present embodiment, since the first reversing roller 62 is disposed at the branch point of the transport path 60 and the duplex transport path 56, the transport path length L1 is set to the above-mentioned length. However, when the bifurcation point between the conveyance path 60 and the duplex conveyance path 56 is slightly before the first reverse roller 62, the conveyance path length L1 is a position where the conveyance path 25 merges with the conveyance path 25 not from the first reversal roller 62 The path length of the double-sided conveyance path 56 up to the point is set.

  If the length L of the sheet 2 in the transport direction is less than the transport path length L1, the alternate transport method can be adopted, and therefore the duplex transport control unit 207 guides the sheet 2 to the first reversing roller 62 and performs reverse transport (S807) . If the length L of the sheet 2 in the transport direction is less than the transport path length L1, the image is formed on the first side, and the sheet reversely transported is newly fed in a state of waiting before merging into the transport path 25. The sheet can be conveyed to the first reversing roller 62. Therefore, printing can be alternately and continuously performed on the sheet 2 fed from the cassette tray 101 and the sheet 2 fed from the double-sided conveyance path 56, and double-sided productivity can be improved. When the length L in the sheet conveyance direction is equal to or more than the conveyance path length L1, the double-sided conveyance control unit 207 performs the same double-sided conveyance control in the first embodiment although the alternate circulation method can not be adopted (S804 to S807).

<Image formation control>
Next, image formation control performed by the image formation control unit 204, which is a feature of the present embodiment, will be described with reference to FIG.

  FIGS. 8A and 8B show the case where three double-sided jobs are executed. FIG. 8A shows the case of performing double-sided printing according to the first embodiment as a comparison, and FIG. 8B shows the conveyance path in which the length L of the sheet 2 in the conveyance direction in the present embodiment is shown in FIG. The case of performing double-sided printing less than the length L1 is shown. Here, the transport speed at the time of image formation is represented by V.

  In the double-sided printing according to the first embodiment, which is a comparative example, as described with reference to FIG. 4, the third sheet fed and discharged at the end after the execution of two double-sided jobs is the normal circulation method. Print is executed under the same image formation control. At this time, the image interval between the first side “1-1” and the second side “1-2” with respect to the sheet fed second and discharged first, and the first side with respect to the third sheet fed and discharged last The image interval between “3-1” and the second surface “3-2” is relatively long. This is because it is necessary to print on the first side of the sheet and then to reverse the sheet by the second reverse sheet ejection roller 52 and to convey it to the conveyance path 25 via the duplex conveyance path 54 and the duplex conveyance path 56 halfway. (Image interval A in FIG. 8A).

  On the other hand, in the present embodiment, when the length L in the transport direction of the sheet 2 is less than the transport path length L1, the sheet to be fed first is transported to the first reverse roller 62, and the second transport is continued. The sheet to be conveyed is also conveyed to the first reverse roller 62. At this time, since the sheet exists at the position of the first reverse roller 62 until the sheet to be fed first reaches the junction before joining the conveyance path 25, the sheet to be fed second is conveyed to the first reverse roller 62. Can not. That is, it is necessary to widen the image interval between the image “1-1” for the sheet to be fed first and the image “2-1” for the sheet to be fed second (“image interval C in FIG. "). Thereafter, the image formation can be performed without the need to widen the image intervals of “2-1”, “1-2”, “3-1”, “2-2” (FIG. 8 (b). Image interval B "). At this time, the double-sided conveyance control unit 207 accelerates the conveyance speed of the sheet 2 during reverse conveyance to shorten the sheet interval. Finally, since the sheet to be fed third is reversed and conveyed in the same flow as in the normal circulation method, the image "3-2" formed on the second side is different from the image "3-1" formed on the first side It is necessary to widen the image interval ("image interval C" in FIG. 8 (b)).

  As described above, in the present embodiment, when the length L in the sheet conveyance direction is less than the conveyance path length L1, the double-sided productivity can be improved by the image interval “(L / V) + B + 2 × compared to double-sided printing according to the first embodiment. (AC) can be enhanced. Here, in the present embodiment, since the time relationship is “{(L / V) + B} / 2> (CA)”, it is effective to improve the both-side productivity. This is because the conveyance time difference (C−A) between the first reverse roller 62 and the second reverse sheet discharge roller 52 is short, and the image formation time (L / V) with respect to the length L in the sheet conveyance direction is long.

  As described above, when the length L in the sheet conveyance direction of the sheet is less than the conveyance path length L1 in this embodiment, the image formation control unit 204 performs “1-1”, “2-1”, and “1-2”. Image formation is performed in the order of "3-1" and "2-2". That is, the image formation is performed on the first side, and the image formation is performed by the alternate circulation method in which the reversely transported sheet and the newly fed sheet are alternately and continuously formed.

  As described above, according to the present embodiment, the double-sided conveyance path to the position where the number of double-sided jobs is three or more and the length in the sheet conveyance direction joins the conveyance path 25 from the first reversing roller 62 If it is shorter than 56, only the first reverse roller 62 is used. And, by performing the image formation by the alternate circulation method, the productivity at the time of double-sided printing can be improved. In addition, even when the length in the sheet conveyance direction is long, the reversing unit is switched so that the sheet to be fed secondly before the sheet to be fed first is discharged to the outside of the machine, and the image forming order is By switching, the productivity at the time of double-sided printing can be improved.

[Example 3]
In the present embodiment, control for further optimizing the control in the first and second embodiments according to the length of the double-sided job in the sheet conveyance direction will be described. The description of the same parts as in the first and second embodiments will be omitted.

<Double-sided conveyance control>
Double-sided conveyance control performed by the double-sided conveyance control unit 207, which is a feature of the present embodiment, will be described with reference to FIGS.

  Whether the double-sided conveyance control unit 207 of the present embodiment operates the double-sided flapper solenoid 223 according to the determination shown in the flowchart of FIG. 9 and guides the sheet 2 to either the first reverse roller 62 or the second reverse paper discharge roller 52 To judge. Upon receiving the print command from the controller 205, the double-sided conveyance control unit 207 determines whether the print command is a double-sided job (S901). Then, when the print job is a single-sided print job, the duplex conveyance control unit 207 guides the sheet 2 to the second reverse sheet ejection roller 52 (S902). If the print job is a double-sided job, then the double-sided conveyance control unit 207 determines whether the length L of the sheet 2 in the conveyance direction is longer than the conveyance path length L2 shown in FIG. 10 (S903). The conveyance path length L2 illustrated in FIG. 10 is returned from the second reverse discharge roller 52 to the second reverse discharge roller 52 via the duplex conveyance path 54, the duplex conveyance path 56, the conveyance path 25, and the conveyance path 63. Distance. That is, it is determined whether or not the length of the sheet 2 in the transport direction is such that the normal circulation system by the second reverse sheet discharge roller 52 can be adopted. In the present embodiment, since the second reverse discharge roller 52 is disposed at the branch point of the conveyance path 63 and the double-sided conveyance path 54, the conveyance path length L2 is set to the above-described length. . However, when the branch point between the conveyance path 63 and the double-sided conveyance path 54 is slightly before the second reverse discharge roller 52, the conveyance path length L2 is from the second reverse discharge roller 52 to the double-sided conveyance path 54, the double-sided conveyance path The route length until returning to the branch point via the transport path 25 and the transport path 63 is set.

  When the length L in the sheet conveyance direction is equal to or less than the conveyance path length L2, as in the first embodiment, the double-sided conveyance control unit 207 controls the odd-numbered sheets to be fed from the cassette tray 101 (for example, the first sheet, It is determined whether it is the third sheet or the like (S904). If the sheet to be fed from the cassette tray 101 is an even-numbered sheet (for example, the second sheet, the fourth sheet, etc.), the duplex conveyance control unit 207 guides the sheet 2 to the second reverse sheet discharge roller 52 and reverses the conveyance. (S905). If the sheet fed from the cassette tray 101 is an odd-numbered sheet, the duplex conveyance control unit 207 determines whether the sheet 2 fed from the cassette tray 101 is a sheet to be fed at the end of the job. (S906). If the sheet to be fed from the cassette tray 101 is a sheet to be fed at the end of the job, the duplex conveyance control unit 207 guides the sheet 2 to the second reverse sheet discharge roller 52 and performs the reverse (S905). If the sheet 2 fed from the cassette tray 101 is not the sheet to be fed at the end of the job, the duplex conveyance control unit 207 guides the sheet 2 to the first reversing roller 62 and carries out reverse conveyance (S907).

  On the other hand, when the length L of the sheet 2 in the conveyance direction exceeds the conveyance path length L2, the duplex conveyance control unit 207 guides the sheet 2 to the first reversing roller 62 and performs reverse conveyance (S907). The reason is that if the length L in the transport direction of the sheet 2 exceeds the transport path length L 2, even if the sheet 2 is reversed and transported using the second reverse sheet discharge roller 52, the second reverse sheet discharge roller 52 This is because the rear end of the sheet 2 is present at the position. That is, the second reverse sheet ejection roller 52 can not be used as the ejection unit. On the other hand, when the first reverse roller 62 is used, since the sheet 2 does not exist at the position of the second reverse sheet discharge roller 52, the second reverse sheet discharge roller 52 can be used as a discharge unit.

<Image formation control>
Next, image formation control performed by the image formation control unit 204, which is a feature of the present embodiment, will be described with reference to FIG.

  FIG. 11 shows the case where two double-sided jobs in which the length L in the transport direction of the sheet 2 in the present embodiment exceeds the transport path length L2 are executed. Since it is necessary to print the first side of the sheet to be fed first and then to reverse it by the first reverse roller 62 and to convey it to the conveyance path 25 via the duplex conveyance path 56, the images of the first and second sides The interval needs to be increased ("image interval C" in FIG. 11). On the other hand, image formation can be performed without widening the image interval of “1-2” and “2-1” (“image interval B” in FIG. 11).

  As described above, in the present embodiment, when the length L in the transport direction of the sheet 2 exceeds the transport path length L2, the image formation control unit 204 performs “1-1”, “1-2”, “2-1”. Image formation is performed in the order of “2-2”. That is, the image formation is performed by the normal circulation method in which the image on the second side is continuously formed after the first side of the fed sheet.

  As described above, according to the present embodiment, the length of the sheet 2 in the transport direction is from the second reverse discharge roller 52 until it returns to the second reverse discharge roller 52 via the plurality of transport paths. If it is longer than the path length, only the first reversing roller 62 is used. Then, double-sided printing can be performed by performing image formation by the normal circulation method. In addition, when the length in the sheet conveyance direction is short, the reversing unit is switched so that the sheet to be fed secondly before the sheet to be fed first is discharged to the outside of the machine, and the image forming order is changed. By switching, the productivity at the time of double-sided printing can be improved.

  Although the examples of the laser beam printer have been described in the above-described first to third embodiments, the image forming apparatus to which the present invention is applied is not limited thereto, and printers of other printing methods such as an inkjet printer, or copying It may be a machine.

9 secondary transfer roller 25 transport path 51 duplex flapper 52 second reverse discharge roller 54 duplex transport path 56 duplex transport path 57 duplex refeed roller 60 transport path 63 transport path 62 first reverse roller 102 sheet feed roller 207 duplex transport Control unit

Claims (7)

Feeding means for feeding the recording material from the placement unit on which the recording material is placed to the first conveyance path;
An image forming unit configured to form an image on a recording material fed from the feeding unit;
Guiding means for guiding a recording material on which an image is formed by the image forming means to either the second conveyance path branched from the first conveyance path or the third conveyance path branched from the first conveyance path;
First reversing means for reversing the transport direction of the recording material transported from the second transport path and transporting the recording material to a first double-sided transport path;
The recording material conveyed from the third conveyance passage is discharged to the outside, or the conveyance direction of the recording material conveyed from the third conveyance passage is reversed, and the recording material is joined in the middle of the first double-sided conveyance passage. Second reversing means for transporting the recording material to the double-sided transport path of
Conveying means for conveying the recording material conveyed to the first duplex conveyance path by the first reversing means or the second reversing means again to the first conveyance path;
When image formation is continuously performed on both sides of a plurality of recording materials, the first recording material is conveyed to the second conveyance path by the guide unit, and a second recording material following the first recording material Before the first recording medium is conveyed to the first duplex conveyance path by the first reversing means, the second reversing means causes the second reversing means to convey the second recording medium. An image forming apparatus having a control unit configured to control the recording material of the recording medium to be conveyed to the first double-sided conveyance path via the second double-sided conveyance path.   The control means causes the second recording material and the first recording material conveyed to the first double-sided conveyance path by the conveyance means to sequentially convey the second recording material to the first conveyance path. The image forming apparatus according to claim 1, wherein the first recording material is controlled to be discharged to the outside after the second recording material is discharged to the outside by the reversing means.   The image forming means interchanges the order of the image formed on the first recording material and the image formed on the second recording material, and the images are respectively formed on the first recording material and the second recording material. The image forming apparatus according to claim 2, wherein the image forming apparatus is formed.   When image formation is continuously performed on both sides of three or more recording materials, and the length of the recording material in the transport direction is from the first reversing means in the first both-side transport path to the first transport path When the distance is shorter than the distance to the joining position, the control unit causes all the recording materials fed by the feeding unit to be conveyed to the second conveyance path by the guiding unit, and the first reversing unit The image forming apparatus according to any one of claims 1 to 3, wherein the control unit controls the recording material to be conveyed to the first double-sided conveyance path.   When image formation is continuously performed on both sides of three or more recording materials, and the length of the recording material in the transport direction is from the first reversing means in the first both-side transport path to the first transport path When it is shorter than the distance to the joining position, the control means alternates from the placing portion and the first both-sided conveyance path in a state where at least one recording material is kept on standby at the first both-sided conveyance path. 5. The image forming apparatus according to claim 4, wherein the image forming apparatus controls the recording material to be conveyed by the image forming unit so as to form an image on each recording material.   The length of the recording material in the transport direction is from the second reversing means to the second duplex transport path, the first duplex transport path, the first transport path, and the second transport path via the third transport path. If the length is longer than the length until returning to the means, the control means causes the recording means to convey all the recording materials fed by the feeding means to the second conveyance path, and the first reversing means The image forming apparatus according to any one of claims 1 to 5, wherein the control unit controls the recording material to be conveyed to the first double-sided conveyance path. The length of the recording material in the transport direction is from the second reversing means to the second duplex transport path, the first duplex transport path, the first transport path, and the second transport path via the third transport path. When the length is longer than the length until returning to the means, the control means causes the guide means to convey the first recording material to the second conveyance path, and the first reversing means causes the first recording material to be conveyed to the second conveyance path. The conveyance means conveys the first recording material to the first conveyance path before conveying the first recording material to the first double-sided conveyance path and feeding the second recording material by the feeding means. The image forming apparatus according to claim 6, characterized in that

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