JP2012137596A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus 1 capable of printing on both sides circularly conveying a recording material P, which solves problems of the rise of temperature at an end part of a fixing part 30 without increasing the size of the apparatus and keeping the productivity thereof.SOLUTION: An image forming apparatus 1 of the present invention comprises: an image processing part 10 for transferring a toner image on an image carrier 11 to a recording material P; a fixing part 30 for fixing the toner image transferred to the recording material P on the recording material P; a paper discharge part 42 for discharging the printed recording material P; an inversion part 41 for inverting two sides of the recording material P; and a circulation conveyance part 40 for re-feeding the inverted recording material P to the image processing part 10. A position of the fixing part 30 through which the recording material P at a first-round passes and a position of the fixing part 30 through which the recording material P at a second-round passes following the circulation conveyance part 40 are made different by shifting the position to the width direction W orthogonal to a conveyance direction S of the recording material P.

Description

  The present invention relates to an image forming apparatus capable of duplex printing while circulating and conveying a plurality of recording materials. The image forming apparatus includes various apparatuses such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions in combination.

  Conventionally, in an image forming apparatus employing an electrophotographic system, a recording material on which an unfixed toner image is transferred is conveyed to a fixing position between a fixing roller heated by a heat source and a pressure roller in contact with the fixing roller. It is widely practiced to fix an unfixed toner image on a recording material by heating and pressurizing (including a so-called heat roller type fixing unit). The fixing roller incorporates a lamp type or induction heating type heater that heats an area corresponding to the maximum sheet passing width. During the fixing process, the entire fixing roller (maximum sheet passing width) is generally heated regardless of the size of the recording material actually conveyed. Here, the sheet passing width means a width direction dimension orthogonal to the recording material conveyance direction.

  When printing a recording material having a width direction length smaller than the maximum sheet passing width of the fixing roller, that is, a so-called small size recording material (for example, A5, A6, B6 size, etc.), a sheet passing portion through which the recording material passes, A non-sheet passing portion that does not occur occurs in the fixing roller. Since heat is not transmitted to the recording material in the non-sheet passing portion of the fixing roller, the temperature of the non-sheet passing portion may increase excessively as compared with the sheet passing portion. The occurrence of the edge temperature rise causes problems such as occurrence of fixing unevenness and wrinkles and hot offset when a large size recording material is printed after a small size recording material is continuously printed. .

  In this regard, in the image forming apparatus described in Patent Document 1, the fixing roller and the pressure roller are moved in the width direction (longitudinal direction) in accordance with the temperatures of the end portion and the center portion of the fixing roller, so that the same fixing roller is used. By avoiding the passage of paper to only the portions, the occurrence of temperature unevenness of the fixing roller and the rise of the edge temperature are suppressed. It is also known to reduce the temperature unevenness of the fixing roller by stopping the heating of the fixing roller between the sheets and causing the fixing roller to idle, or by reducing the process speed (printing speed).

JP 2009-175344 A

  However, in the configuration of Patent Document 1, since it is necessary to move the fixing roller and the pressure roller in the width direction, the size of the image forming apparatus is increased. Further, in the prior art, since the fixing roller is idled or the process speed is lowered, there is a problem that the number of printed sheets per unit time has to be reduced and productivity is lowered. The present invention has been made in view of the above-mentioned problems, and it is a technical problem to solve the problem of an increase in the end portion temperature of the fixing unit while not increasing the size of the apparatus and maintaining productivity. To do.

  According to a first aspect of the present invention, there is provided an image processing unit that transfers a toner image on an image carrier onto a recording material, a fixing unit that fixes the toner image transferred onto the recording material to the recording material, and a printed recording material. An image forming apparatus comprising: a paper discharge unit that discharges; a reversing unit that reverses the recording material, and a circulation conveyance unit that refeeds the recording material that has been turned upside down to the image processing unit. A position in which the recording material of the second pass passes through the fixing unit and a position in which the recording material of the second pass through the circulation transport unit passes through the fixing unit in a width direction orthogonal to the transport direction of the recording material. It is to make it different by shifting.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the circulating conveyance unit has a passage position changing mechanism for changing a passage position of the recording material with respect to the fixing unit.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, if the length of the recording material in the width direction is not less than half of the maximum sheet passing width, the first recording material and the second recording material are recorded. If the width of the recording material is less than half of the maximum sheet passing width, the recording material for the first round and the recording material for the second round are aligned. It is conveyed to the image processing unit.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the selection of the alternate conveyance or the aligned conveyance is performed according to the length in the width direction of the recording material.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the third or fourth aspect, the switching member for switching between guiding the recording material after passing through the fixing unit to the reversing unit or the paper discharging unit. Are arranged side by side in the width direction, and each of the switching members guides the recording material of the first round to the reversing portion and guides the recording material of the second round to the paper discharge portion, They can be switched independently of each other.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, when printing is performed only on one side of the recording material, the recording material is conveyed to the circulation conveyance unit, and the fixing unit performs the first round. The paper is discharged after passing through different passing positions.

  According to the invention described in the claims of the present application, the second-round recording material on which the unfixed toner image is placed on the other side takes heat away from the passing position with respect to the fixing portion during the fixing process. The passing position is shifted in the width direction from the passing position of the first recording material. That is, in the fixing unit, the passing position of the first recording material and the passing position of the second recording material are deviated in the width direction and take heat in different ranges. Accordingly, it is possible to easily avoid passing through only the same portion of the fixing unit without causing an increase in the size of the apparatus as in the prior art, and occurrence of temperature unevenness in the fixing unit and an increase in end temperature. There is an effect that can be suppressed.

It is a schematic explanatory drawing of a printer. It is a block diagram which shows the structure of a control part. It is a schematic explanatory drawing which shows the conveyance state of the circulation conveyance part at the time of alternating conveyance double-sided printing. FIG. 6 is a schematic explanatory diagram illustrating a conveyance state of a fixing unit during alternate conveyance duplex printing. It is a schematic explanatory drawing which shows the conveyance state of the circulation conveyance part at the time of a row conveyance double-sided printing. FIG. 6 is a schematic explanatory diagram illustrating a conveyance state of a fixing unit at the time of aligned conveyance duplex printing. FIGS. 4A and 4B are explanatory diagrams of driving of a path switching gate at the time of alternate conveyance double-side printing, in which FIG. 5A shows a case of guiding to a pair of reversing rollers, and FIG. It is drive explanatory drawing of the path | route switching gate at the time of a row conveyance double-sided printing. It is a flowchart which shows an example of passage position change control. It is a flowchart which shows another example of passage position change control.

  Hereinafter, an embodiment in which the present invention is applied to a tandem color digital printer (hereinafter referred to as a printer), which is an example of an image forming apparatus, will be described with reference to the drawings.

  As shown in FIG. 1, the printer 1 has a circulation type double-sided printing function, and includes an image processing unit 10, a feeding unit 20, a fixing unit 30, a circulating conveyance unit 40, a control unit 60, and the like. Although illustration is omitted, the printer 1 is connected to a network such as a LAN, for example, and receives a print command from an external terminal (not shown) which is an example of an external device, and then prints a print job based on the print command. Is configured to run. The print job includes a job in a single-side mode for printing (image formation) on one side of the recording material P and a job in a double-side mode for printing on one side and the other side of the recording material P.

  The image processing unit 10 plays a role of transferring a toner image formed on a photosensitive drum 3 which is an example of an image carrier to a recording material P, and includes yellow (Y), magenta (M), cyan ( A total of four image forming units 2 corresponding to the respective colors C) and black (K), an intermediate transfer belt 11 and the like are provided. The four image forming units 2 are arranged below the intermediate transfer belt 11 along the intermediate transfer belt 11 in the order of yellow, magenta, cyan, and black) from the left in FIG. Each image forming unit 2 includes a photosensitive drum 3 that is driven to rotate clockwise in FIG. Around the photosensitive drum 3, a charging unit 4, an exposure unit 5, a developing unit 6, a primary transfer roller 7, and a photoconductor cleaner 8 are arranged in this order along the rotation direction (clockwise in FIG. 1). Yes. In FIG. 1, for convenience of explanation, symbols Y, M, C, and B corresponding to reproduced colors are attached to each image forming unit 2. Further, in the image forming units 2M to 2K other than the yellow image forming unit 2Y, the reference numerals 3 to 8 of the respective components such as the photosensitive drum 3 are omitted.

  The intermediate transfer belt 11 is also an example of an image carrier, and is wound around a driving roller 12, a driven roller 13, and a tension roller 14. The intermediate transfer belt 11 is driven to rotate counterclockwise in FIG. A secondary transfer roller 25, which is a component of the feeding unit 20, is disposed outside the portion of the intermediate transfer belt 1 that is wound around the drive roller 12. A contact portion between the intermediate transfer belt 11 and the secondary transfer roller 25 is a secondary transfer position 15. A transfer belt cleaner 16 for removing untransferred toner on the intermediate transfer belt 11 is disposed outside the portion of the intermediate transfer belt 11 that is wound around the driven roller 13. Note that the length in the width direction of the intermediate transfer belt 11 is slightly longer than the length in the width direction 297 mm of the A3 vertical recording material P so that it can be transferred to the A3 vertical recording material P.

  The feeding unit 20 includes a paper feeding cassette 21 that accommodates the recording material P, a pair of paper feeding rollers 22 that feeds the recording material P in the paper feeding cassette 21 one by one toward the main transport path R0, and a fed recording material P. Are provided with a registration roller pair 24, a secondary transfer roller 25, and the like that take the timing of feeding the recording material P to the secondary transfer position 15. The recording material P from the paper feed cassette 21 is sent to the main transport path R0 via the paper feed path R1 by the rotational drive of the paper feed roller pair 22. The sheet feed path R1 joins the main transport path R0 on the transport upstream side of the registration roller pair 24. The recording material P in the paper feed cassette 21 has one side end extending in the transport direction S along the reference line SL (see FIGS. 3 to 6), and the one-side reference fed out to the paper feed path R1 based on the reference line SL. Set to Therefore, the transfer process in the image process unit 10 and the fixing process in the fixing unit 30 are also executed on a one-side basis.

  Note that the printer 1 of the embodiment is a so-called A3 compatible machine, and is a longitudinal feeding device in which a maximum A3 size recording material P enters the paper cassette 21 from the short side into the image processing unit 10 or the fixing unit 30. It can be accommodated in a posture. In this case, the width dimension length of the A3 vertical recording material P is 297 mm, and the length in the transport direction is 420 mm.

  The fixing unit 30 includes a fixing roller 31 including a fixing heater 33 such as a halogen lamp, and a pressure roller 32 facing the fixing roller 31. A contact portion between the fixing roller 31 and the pressure roller 32 is a fixing position. The controller 60 controls the energization of the fixing heater 33 so that the fixing heater 33 is maintained at a temperature necessary for fixing. In this case, the heating portion length of the fixing heater 33 with respect to the fixing roller 31 is set slightly longer than the length 297 mm in the width direction of the A3 vertical recording material P so that the A3 vertical recording material can be heated. As can be seen from the relationship between the heating portion length of the fixing heater 33 with respect to the fixing roller 31 and the width direction length of the intermediate transfer belt 11, the maximum sheet passing width Wmx of the printer 1 is a length that can be printed on the A3 vertical recording material P. Is set. Specifically, the length in the width direction of the A3 vertical recording material P is slightly longer than 297 mm, for example, about 300 mm.

  The circulation conveyance unit 40 includes a reverse roller pair 41 as a reverse unit that reverses the recording material P after single-sided printing, a discharge roller pair 42 as a paper discharge unit that discharges the printed recording material P, and a plurality of both surfaces. A pair of conveyance rollers 43 to 46. In the circulation conveyance unit 40, the recording material P after single-sided printing is turned upside down and conveyed again to the registration roller pair 24 via the circulation conveyance path R2. The reversing roller pair 41 is configured to be able to rotate forward and backward, and can discharge the recording material P out of the printer 1 or switch back (reversely feed) it back into the printer 1. Note that a storage tray 51 for the reverse roller pair 41 and a paper discharge tray 52 for the discharge roller pair 42 are provided on the upper portion of the printer 1. The printed recording material P is discharged onto the discharge tray 52 by the rotation drive of the discharge roller pair 42. It goes without saying that the printed recording material P can be discharged onto the storage tray 51 by the rotation of the pair of reverse rollers 41.

  The terminal side of the main transport path R0 extends toward the discharge roller pair 42. On the other hand, the starting end side of the circulation conveyance path R <b> 2 extends toward the reverse roller pair 41. The terminal end side of the main transport path R0 and the start end side of the circulation transport path R2 are arranged in parallel vertically. Between the terminal end side of the main transport path R0 and the start end side of the circulation transport path R2, a path switching gate 47a as a switching member that switches between sending the recording material P to the reverse roller pair 41 or the discharge roller pair 42, A pair 47b is provided side by side in the width direction W (direction perpendicular to the conveyance direction S of the recording material P, see FIGS. 7 and 8).

  As will be described in detail later, each path switching gate 47a, 47b closes the terminal end side of the main transport path R0 to the start end side of the circulation transport path R2 by excitation of each solenoid 70a, 70b connected to the control unit 60. The connected state (the state in which the recording material P is guided toward the reversing roller pair 41) and the state in which the terminal end side of the main transport path R0 is opened and separated from the start end side of the circulation transport path R2 (recording toward the discharge roller pair 42) The state in which the material P is guided) is driven to be switched. The path switching gates 47a and 47b are configured to be switchable independently of each other. The width dimension of each path switching gate 47a, 47b is set to half the maximum sheet passing width Wmx of the printer 1 (see FIGS. 7 and 8).

  For example, when the A3 size recording material P is switched back by the reverse roller pair 41 to the start end side of the circulation conveyance path R2, the recording material P is conveyed toward the circulation conveyance path R2. At this time, the communication between the terminal end side of the main transport path R0 and the start end side of the circulation transport path R2 is interrupted by the switching drive of both the path switching gates 47a and 47b. The terminal end side of the circulation conveyance path R3 joins the main conveyance path R0 on the conveyance upstream side of the registration roller pair 24.

  As shown in FIGS. 3 and 5, the second and third ones 44 and 45 from the upstream side of the plurality of double-sided conveying roller pairs 43 to 46 change the passage position of the recording material P with respect to the fixing unit 30. The swing roller pair 44, 45 is a component of the position changing mechanism. The swing roller pair 44, 45 is configured to be able to change the angle θ with respect to the width direction W. A drive unit (not shown) such as a rack and a pinion for changing the angle is provided at one axial end of both the swing roller pairs 44 and 45. For example, when the rack reciprocates along the transport direction S by the rotation of the pinion, both the swing roller pairs 44 and 45 swing with the other end in the axial direction as a fulcrum while being parallel to each other. Thus, the angle θ with respect to the width direction W is changed. The passing position of the recording material P transported to the circulation transport path R2 is changed from the one-side reference state by the two swing roller pairs 44 and 45 having the angle θ changed, and the first round (before passing through the circulation transport unit 40). The passing position of the recording material P and the passing position of the recording material P in the second round (after passing through the circulation conveyance section 40) can be shifted in the width direction W to be different.

  As shown in FIG. 1, a pair of recording material sensors 55a and 55b as recording material detecting means for detecting the passage of the recording material P is disposed on the downstream side of the fixing unit 30 in the main transport path R0 ( FIG. 1 shows only the front side 55b). In the embodiment, a pair of recording material sensors 55a and 55b are arranged on both sides of the center of the maximum sheet passing width Wmx (see FIGS. 4 and 6). The arrangement interval in the width direction of both recording material sensors 55a and 55b is such that when the A4 vertical recording material P passes by one side reference, the first recording material sensor 55a is turned on, but the second recording material sensor 55b is turned off. Is set to the positional relationship. As each of the recording material sensors 55a and 55b, for example, a photo sensor that optically detects passage of the recording material P, a contact type limit switch, or the like is employed.

  The printing operation of one A3 size recording material P in the single-side mode is performed as follows. That is, for each of the image forming units 2Y to 2K, the photosensitive drum 3 cleaned by the photosensitive member cleaner 8 is uniformly charged by the charging unit 4, and the surface of the photosensitive drum 3 is exposed by exposure from the exposure unit 5. An electrostatic latent image is formed on the surface. The electrostatic latent image is reversely developed with toner from the developing unit 6 and is visualized as a toner image of each color. The toner images of the respective colors are primarily transferred from the photosensitive drum 3 onto the intermediate transfer belt 11 in the order of yellow, magenta, cyan, and black by the primary transfer roller 7 and are superimposed. On the other hand, the recording material P is conveyed to the secondary transfer position 15 by the registration roller pair 24 in accordance with the movement timing of each color toner image toward the secondary transfer position 15 by the rotational drive of the intermediate transfer belt 11. When the recording material P passes through the secondary transfer position 15, the overlapping four color toner images are collectively transferred onto one side of the recording material P. The intermediate transfer belt 11 after the secondary transfer is cleaned by a transfer belt cleaner 12. The recording material P that has passed through the secondary transfer position 15 and has an unfixed toner image on one side is heated and pressurized when passing through the fixing unit 30 to fix the unfixed toner image. In the fixing process, the terminal end side of the main transport path R0 is opened by the switching drive of both the path switching gates 47a and 47b, and communication between the terminal end side of the main transport path R0 and the start end side of the circulation transport path R2 is blocked. . The recording material P after single-sided fixing (printed) is discharged onto the paper discharge tray 52 by the rotational drive of the discharge roller pair 42.

  The printing operation of one A3 size recording material P in the duplex mode is performed as follows. That is, at the start of single-sided printing, the end side of the main transport path R0 is closed by the switching drive of both path switching gates 47a and 47b, and the main transport path R0 is connected to the start end side of the circulation transport path R2. The recording material P after single-sided printing is conveyed toward the reverse roller pair 41. Immediately before the rear end side of the conveyance of the recording material P passes the reversing roller pair 41, the reversing roller pair 41 is driven in reverse to switch back the recording material P after single-sided printing, and the recording material is reversed upside down with respect to the image processing unit 10. P is introduced into the circulation conveyance path R2. The recording material P conveyed to the circulation conveyance path R2 is returned again to the main conveyance path R0 by the rotational drive of the double-sided conveyance roller pair 43 to 46, and again to the secondary transfer position 15 by the rotation drive of the registration roller pair 24. It is sent. In this case, the swing roller pairs 44 and 45 are held in a state parallel to the width direction W without changing the angle θ. In conjunction with the circulating conveyance, the image processing unit 10 performs primary transfer of each color toner image on the other surface of the re-recorded recording material P, and each color toner image superimposed on the intermediate transfer belt 11 is transferred. At the secondary transfer position 15, secondary transfer is performed collectively on the other surface of the recording material P. The recording material P on which the unfixed toner image is placed on the other side is fixed by the fixing unit 30. Then, the rear end side of the main transport path R0 is opened by the switching drive of the both path switching gates 47a and 47b, and the recording material P after the other side fixing (double-sided printing) is discharged by the rotation driving of the discharge roller pair 42. The paper is discharged onto the paper tray 52.

  In the double-sided mode, as the double-sided printing function of the circulation type, when double-sided printing of a plurality of recording materials P is performed continuously, single-sided printing and other-sided printing are executed with a predetermined number of circulating sheets as one unit. Is set to repeat printing. For example, if the number of circulating sheets is four, four recording materials P are continuously printed on one side, then reversed and conveyed in a circulating manner, and the other side of the four recording materials P is printed. For example, when performing double-sided printing of a plurality of A3 size recording materials P, the main transport path R0 is connected to the starting end side of the circulation transport path R2 by switching driving of both path switching gates 47a and 47b, and an image is formed on one side of the recording material P. Print odd pages of data in order. Then, the terminal end side of the main transport path R0 is opened by switching driving of both the path switching gates 47a and 47b, and even pages of the image data are sequentially printed on the other surface of the recording material P. P is discharged onto the discharge tray 52 by the discharge roller pair 42.

  The control unit 60 receives an image signal transmitted from an external terminal (not shown), converts the image signal into digitized image data for Y to K colors, and the image processing unit 10 and the feeding unit 20. The printing operation is executed by controlling each operation unit such as. The control unit 60 according to the embodiment is disposed between the image processing unit 10 and the paper feed cassette 21 in the printer 1. The controller 60 includes a controller 61.

  In addition to the CPU 62 that executes various arithmetic processes and controls, the controller 61 temporarily stores a communication interface (I / F) unit 63 for connection with an external terminal, storage means 64 such as an EEPROM or flash memory, control programs and data. RAM 65 to be stored, a counter 66 for measuring the number of conveyed recording materials P, a timer 67 for measuring time, an input / output interface, and the like. The input / output interface of the controller 61 includes, for example, first and second recording material sensors 55a and 55b that detect passage of the recording material P, and first and second solenoids 70a and 70b that drive the path switching gates 47a and 47b, A drive circuit 56 that drives a drive unit for both the swing roller pairs 44 and 45, an operation panel 57 mounted on the exterior of the printer 1, and the like are electrically connected.

  The controller 61 is configured to execute passage position change control for changing the passage position of the recording material P in the width direction W according to the width direction length Wp in the duplex mode. FIG. 9 shows an example of passage position change control by the control unit 60. The algorithm shown in the flowchart disclosed below is stored in advance in the storage unit 64 of the controller 61 as a program, and is read by the RAM 65 and then executed by the CPU 62. Here, as the print setting of the printer 1, it is assumed that the duplex mode is designated in advance by a print command from an external device such as the operation panel 57 or an external terminal.

  In this case, information on the size of the recording material P and the number of printed sheets included in the print command from the external device is acquired (S01). Then, it is determined whether the number of printed sheets is equal to or larger than a predetermined number set in advance and the width direction length Wp of the recording material P obtained from the size information is equal to or larger than 297 mm (A3 length or A4 width) (S02). . In this case, the predetermined number is, for example, about 10. When the number of printed sheets is equal to or greater than the predetermined number and the width direction length Wp is equal to or greater than 297 mm (S02: YES), normal duplex printing is executed (S03).

  That is, as described above, the main conveyance path R0 is connected to the start end side of the circulation conveyance path R2 by the switching drive of both the path switching gates 47a and 47b, and the odd pages of the image data are sequentially printed on one side of the recording material P. . Then, the terminal side of the main transport path R0 is opened by switching drive of both the path switching gates 47a and 47b, and the recording material P that is turned upside down is returned to the main transport path R0 again via the circulation transport path R2, and the recording material P The even pages of the image data are printed in order on the other side. Needless to say, the swing roller pair 44, 45 is in a state parallel to the width direction W without changing the angle θ. Then, the double-side printed recording material P is discharged onto the discharge tray 52 by the discharge roller pair 42.

  If the condition is not satisfied in step S02 (S02: NO), it is then determined whether or not the width direction length Wp of the recording material P is not less than half of the maximum sheet passing width Wmx (for example, not less than about 150 mm) (S04). If the width direction length Wp is more than half of the maximum sheet passing width Wmx (S04: YES), the recording material P in the first round (before passing through the circulating transport section 40) and the second round (after passing through the circulating transport section 40). The recording material P is alternately conveyed to the image processing unit 10 and alternate conveyance duplex printing is executed (S05). If the length Wp in the width direction is less than half of the maximum sheet passing width Wmx (S04: NO), the image processing unit 10 arranges the recording material P for the first round and the recording material P for the second round side by side (simultaneously in parallel). Next, the side-by-side transport double-sided printing is executed (S06).

  The alternating conveyance duplex printing in step S05 is performed as follows. That is, the main transport path R0 is connected to the start end side of the circulation transport path R2 by switching driving of both the path switching gates 47a and 47b (see FIG. 7A), and odd pages of image data are sequentially placed on one side of the recording material P. To print on. Then, the recording material P that has been switched back is returned to the main transport path R0 via the circulation transport path R2. At this time, the angle θ with respect to the width direction W of both the swing roller pairs 44 and 45 is changed, and the recording material P transported to the circulation transport path R2 by the both swing roller pairs 44 and 45 having the changed angle θ is a reference. The recording material P, which is conveyed in an oblique direction away from the line SL (see FIG. 3), is interrupted after being fed from the registration roller pair 24 and stopped by the registration roller pair 24. The passing position of the recording material P that has reached the second round at this stage is shifted in the width direction W from the passing position of the recording material P in the first round (before passing through the circulation conveyance section 40), although a part of the overlap occurs. And located closer to the second recording material sensor 55b.

  Thereafter, as shown in FIG. 4, the registration roller pair 24 is driven, and the second recording material P located near the second recording material sensor 55b is sent out. While the even pages of the image data are printed in order, the odd pages of the image data are successively printed on one side of the first recording material P located near the first recording material sensor 55a. In this case, at the transfer position 15, the first recording material P → the second recording material P → the first recording material P → the second recording material P. The recording material P and the recording material P in the second round are alternately fed until all printing is completed.

  The recording material P in the second round on which the unfixed toner image is placed on the other side is fixed by the fixing unit 30 and takes heat from the passing position at the fixing unit 30. At that time, the passing position of the recording material P in the second round is shifted in the width direction W from the passing position of the recording material P in the first round and is positioned closer to the second recording material sensor 55b, although a part of the overlap occurs. is doing. That is, in the fixing unit 30, the passing position of the first recording material P and the passing position of the second recording material P are shifted in the width direction W and take heat in different ranges. Accordingly, it is possible to easily avoid passing the paper through only the same portion of the fixing unit 30 without increasing the size of the apparatus as in the prior art, and occurrence of temperature unevenness of the fixing unit 30 and occurrence of an end temperature increase. Can be suppressed. In addition, even when the number of printed sheets is large, the recording material P in the first round and the recording material P in the second round pass through the fixing unit 30 alternately from the middle of printing, resulting in an increase in end temperature. There is also an advantage that the fixing unit 30 can be prevented from being damaged.

  When the first recording material P and the second recording material P are alternately conveyed to the fixing unit 30, the first recording material sensor 55a is on and the second recording material sensor 55b is off. (Refer to FIG. 4) This means that the recording material P is passing through the first round, so the main transport path R0 is connected to the start end side of the circulation transport path R2 by the switching drive of both path switching gates 47a and 47b (FIG. 7 ( a)), the recording material P of the first round after single-sided printing is switched back and introduced into the circulation conveyance path R2. If the first recording material sensor 55a is off and the second recording material sensor 55b is on, it means that the recording material P is passing through the second round. Therefore, the switching drive of both the path switching gates 47a, 47b is the main driving. The end side of the transport path R0 is opened (see FIG. 7B), and the recording material P after fixing the other side (printed on both sides) is discharged onto the discharge tray 52 by the rotational drive of the discharge roller pair 42. It will be.

  The aligned transport duplex printing in step S06 is performed as follows. That is, the main conveyance path R0 is connected to the starting end side of the circulation conveyance path R2 by the switching drive of the first path switching gate 47a (see FIG. 8), and odd pages of image data are sequentially printed on one side of the recording material P. Go. In this case, the second path switching gate 47b is maintained in a state where the terminal side of the main transport path R0 is opened (see FIG. 8). Then, the recording material P that has been switched back is returned to the main transport path R0 via the circulation transport path R2. At that time, the angle θ ′ with respect to the width direction W of both the swing roller pairs 44 and 45 is changed, and the recording material P transported to the circulation transport path R2 by the both swing roller pairs 44 and 45 having the angle θ ′ changed. Is conveyed in an oblique direction away from the reference line SL (see FIG. 5), the recording material P being conveyed in the first round is interrupted by the registration roller pair 24 and stopped. The passing position of the recording material P that has reached the second round at this stage is shifted in the width direction W from the passing position of the recording material P in the first round (before passing through the circulation conveyance section 40) without overlapping, and the second recording. It is located closer to the material sensor 55b.

  After that, as shown in FIG. 6, the registration roller pair 24 is driven, and the second recording material P located near the second recording material sensor 55b and the first round located near the first recording material sensor 55a. The recording material P is sent out simultaneously in parallel, and an even page of image data is printed on the other surface of the recording material P in the second round, while an odd page of image data is printed on one side of the recording material P in the first cycle. In this case, at the transfer position 15, the first recording material P and the second recording material P → the first recording material P, the second recording material P. The recording material P and the recording material P in the second round are sent simultaneously in parallel until all printing is completed.

  The first and second recording materials P arranged in the width direction W are fixed by the fixing unit 30, and heat is taken away from the passing position in the fixing unit 30. Accordingly, in this case as well, in the fixing unit 30, the passing position of the first recording material P and the passing position of the second recording material P are shifted in the width direction W and take heat in different ranges. Accordingly, it is possible to easily avoid passing the paper through only the same portion of the fixing unit 30 without increasing the size of the apparatus as in the prior art, and occurrence of temperature unevenness of the fixing unit 30 and occurrence of an end temperature increase. Can be suppressed. Further, since the two recording materials P are simultaneously printed in parallel, the productivity of the recording material P having the width direction length Wp less than half the maximum sheet passing width Wmx can be remarkably improved. In addition, even when the number of printed sheets is large, since the first recording material P and the second recording material P pass through the fixing unit 30 simultaneously in the middle of printing, the width direction length Wp is the maximum sheet passing width. Even the recording material P (so-called small-size recording material P) that is less than half of Wmx can take heat from a wide range of the fixing unit 30, and damage to the fixing unit 30 due to an increase in the end temperature is caused in advance. Can be prevented. The recording material P in the second round after duplex printing is discharged onto the discharge tray 52 by the rotational drive of the discharge roller pair 42 from the end side of the main transport path R0 opened by the second path switching gate 47b. Will be.

  FIG. 10 shows another example of passing position change control by the control unit 60. In the above-described example, the control mode in the duplex mode has been described. However, the present invention is not limited to this, and the passing position of the recording material P in the first round and the second round are also passed through the circulation conveyance unit 40 in the single-sided mode. A mode in which the passing position of the eye recording material P is shifted in the width direction W is possible. In this case, when the recording material P in the second round passes through the transfer position 15, only the point that nothing is printed on the other surface side is different from the above example, and the other control is the same as the above example. Is. Accordingly, even in another example, it is possible to easily avoid passing the paper through the same portion of the fixing unit 30 without increasing the size of the apparatus as in the prior art, and the occurrence of temperature unevenness and the end of the fixing unit 30 can be avoided. It is possible to suppress the occurrence of an increase in the part temperature.

  The present invention is not limited to the above-described embodiment, and can be embodied in various forms. For example, a printer has been described as an example of the image forming apparatus. However, the present invention is not limited to this, and a copier, a facsimile, or a multifunction machine having these functions combined may be used. The transfer method is not limited to the intermediate transfer method employed in the embodiment, and may be a direct transfer method. Further, although the tandem method is adopted in the embodiment, a multi-rotation method may be adopted. In addition, the configuration of each unit is not limited to the illustrated embodiment, and various modifications can be made without departing from the spirit of the present invention.

P Recording material R0 Main transport path R1 Paper feed path R2 Circulation transport path S Transport direction W Width direction Wmx Maximum sheet feed width Wp Width direction length 1 Printer (image forming apparatus)
DESCRIPTION OF SYMBOLS 10 Image process part 20 Feed part 30 Fixing part 40 Circulation conveyance part 60 Control part 61 Controller

Claims (6)

An image processing unit that transfers a toner image on the image carrier to a recording material, a fixing unit that fixes the toner image transferred to the recording material to the recording material, a paper discharge unit that discharges the printed recording material, An image forming apparatus comprising a reversing unit for reversing the recording material, and a circulation conveying unit for refeeding the recording material that has been reversed to the image processing unit,
A width direction perpendicular to the conveyance direction of the recording material is a position where the recording material of the first round passes the fixing unit and a position where the recording material of the second round via the circulation conveyance unit passes the fixing unit. To make it different,
Image forming apparatus. The circulation conveyance unit has a passage position changing mechanism for changing the passage position of the recording material with respect to the fixing unit.
The image forming apparatus according to claim 1. If the length in the width direction of the recording material is not less than half of the maximum sheet passing width, the recording material for the first round and the recording material for the second round are alternately conveyed to the image processing unit,
If the length in the width direction of the recording material is less than half of the maximum sheet passing width, the recording material for the first round and the recording material for the second round are conveyed side by side to the image processing unit.
The image forming apparatus according to claim 1. The selection of the alternate conveyance or the aligned conveyance is performed according to the length in the width direction of the recording material.
The image forming apparatus according to claim 3. A pair of switching members are provided side by side in the width direction for switching whether to guide the recording material after passing through the fixing unit to the reversing unit or to the paper discharge unit,
The switching members can be switched independently of each other so as to guide the recording material of the first round to the reversing unit and guide the recording material of the second round to the paper discharge unit.
The image forming apparatus according to claim 3 or 4. When printing only on one side of the recording material, the recording material is transported to the circulation transport unit, and discharged after passing through a different pass position from the first round in the fixing unit.
The image forming apparatus according to claim 1.

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