JP2009075478A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which has simple configuration, is inexpensive and can prevent skewing of a sheet. <P>SOLUTION: A fixing unit 20 is provided with an inverting roller pair 24 and a double-sided conveyance rollers 25a. When a door unit 40 forming a double-sided conveyance path 41 is closed, a positioning part positions the double-sided conveyance rollers 25b of a door unit side disposed in the door unit 40 with respect to the double-sided conveyance roller 25a disposed in the fixing unit 20, the double-sided conveyance rollers 25b of the door unit side being rollers other than the rollers disposed in the fixing unit 20. This makes it possible to reduce misalignment between a fixing means 21, the double-sided conveyance roller pair 25 and the inverting roller pair 24. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an apparatus in which a sheet on which a toner image is fixed is conveyed again to an image forming unit.

  Conventionally, in image forming apparatuses such as printers, copiers, and fax machines, in addition to a mode in which an image is formed on one side (first side) of a sheet, an image is formed on the back side (second side) of a sheet on which an image is formed on one side. Some have a double-sided mode to form

  In such an image forming apparatus, a sheet reversing mechanism is provided, and in the double-side mode, the sheet is reversed so that an image is formed on the back side opposite to the sheet on which the image is formed on one side by the image forming unit. Then, it is conveyed again to the image forming unit.

  FIG. 9 is a diagram showing a configuration of a conventional image forming apparatus provided with such a sheet reversing mechanism. In this image forming apparatus, when an image is formed on a sheet, first, the sheet S1 stored in the sheet feeding cassette 110 serving as a sheet stacking unit is fed by the feeding roller 111. Thereafter, the fed sheet S1 is sent to image forming units 102a to 102d that form yellow, magenta, cyan, and black toner images via a registration roller 113 having a skew feeding correction function and an electrostatic transfer belt 114. The toner image is transferred onto the sheet.

  Next, the sheet S on which the toner image has been transferred is conveyed to the fixing unit 115 and is heated under pressure in the fixing unit 115 to fix the toner image, and then passes through the paper discharge / reverse roller pair 116. The paper is discharged to the paper discharge tray 117.

  When the double-side mode for forming both images on the back side is selected, the fixing unit 115 fixes the toner image on one side as described above, and then the sheet S1 is conveyed to the paper discharge / reverse roller pair 116. Is done. Next, the sheet S1 discharged in the direction of the discharge tray 117 by the discharge / reverse roller pair 116 is reversed by the discharge / reverse roller pair 116 before the entire sheet is discharged to the discharge tray 117. The sheet S1 is conveyed to the double-sided conveyance path 118 with the rear end of the sheet S1 as the head.

  Next, the sheet S1 is conveyed again to the registration roller pair 113 by the conveyance roller pairs 119 to 122 provided in the double-sided conveyance path 118. After the skew feeding is corrected by the registration roller pair 113, the sheet S1 is statically moved. The sheet is fed again to the electrotransfer belt 114. Next, an image is formed on the back surface of the sheet S1 in each color image forming unit 102a to 104d, and after the toner image is fixed by the fixing unit 115, the paper discharge tray 117 passes through the paper discharge / reverse roller pair 116. Is discharged.

  In FIG. 9, reference numeral 115A denotes a fixing unit, and the fixing unit 115 is attached to the fixing unit 115A. The paper discharge / reverse roller pair 116 is provided in the image forming apparatus main body 101, and the double-sided conveyance roller pair 119 provided in the double-sided conveyance path 118 is provided in a door (not shown) that can be opened and closed.

  That is, the fixing unit 115 that conveys the sheet S1, the paper discharge / reverse roller pair 116, and the double-sided conveyance roller pair 119 are provided in separate units. Here, when they are provided in separate units as described above, the number of parts interposed between the fixing unit 115, the paper discharge / reverse roller pair 116, and the duplex conveying roller pair 119 increases. When the number of intervening parts increases as described above, the alignment of the fixing unit 115, the paper discharge / reverse roller pair 116, and the double-sided conveying roller pair 119 is displaced, which causes skewing.

  In order to prevent such skewing, for example, a clutch mechanism for controlling drive transmission to the double-sided conveyance roller pair 119 provided in the double-sided conveyance path 118 and a sheet immediately before the double-sided conveyance roller pair 119 are detected. In some cases, a skew correction unit including a sensor is provided.

  The skew feeding correction unit stops the driving of the duplex conveying roller pair 119 until the sensor detects the sheet. When the sensor detects the sheet, after that, after a predetermined time, the clutch mechanism causes the duplex conveying roller pair 119 to move. I try to drive it. Then, after the sensor detects the sheet in this way, after a predetermined time has elapsed, the skew feeding of the sheet can be corrected by driving the duplex conveying roller pair 119 (see Patent Document 1).

  In addition, in order to prevent skew feeding, there are also proposed ones in which a shutter is disposed on the duplex conveying roller pair 119, or the sheet is skewed by the pair of skew feeding rollers so as to follow the reference guide. ing.

JP 2003-155146 A

  However, in such a conventional image forming apparatus, when a clutch mechanism and a sensor are provided in the double-sided conveyance path, the configuration becomes complicated and the number of parts increases, resulting in an increase in cost. This also applies to the case where a skew feeding roller and a shutter mechanism are arranged on the double-sided conveyance path.

  Therefore, the present invention has been made in view of such a situation, and an object thereof is to provide an image forming apparatus that can prevent sheet skewing with a simple configuration and at low cost. is there.

  The present invention provides an image forming unit for forming a toner image, a fixing unit having a fixing member for fixing the toner image transferred to the sheet to the sheet, and the sheet on which the toner image is fixed again to the image forming unit. A re-conveying path for conveying the toner image, a reversible conveying roller pair capable of reversing and conveying the sheet on which the toner image is fixed to the re-conveying path, and the re-conveying path. An image forming apparatus comprising: a pair of conveying rollers that conveys a sheet that is reversed and conveyed by a pair of rollers toward the image forming unit, wherein the fixing unit is detachably provided in a main body of the image forming apparatus, and the inversion At least one roller constituting the conveyance roller pair and at least one roller constituting the conveyance roller pair are arranged in the fixing unit.

  According to another aspect of the present invention, there is provided an image forming unit that forms a toner image, a fixing unit that includes a fixing member that fixes the toner image transferred to the sheet to the sheet, and the sheet on which the toner image is fixed again to the image. A re-conveying path for conveying to the forming unit, a reversible conveying roller pair capable of reversing and conveying the sheet on which the toner image is fixed and conveyed to the re-conveying path, and the re-conveying path, A pair of conveyance rollers that conveys a sheet that is reversed and conveyed by a reverse conveyance roller toward the image forming unit, and a door member that forms the re-conveyance path and that can be opened and closed in the image forming apparatus main body. In the image forming apparatus, at least one roller constituting the reverse conveyance roller pair and at least one roller constituting the conveyance roller pair are disposed in the fixing unit, and the reverse conveyance is performed. Among the rollers constituting the roller pair and the conveying roller pair, rollers other than those arranged in the fixing unit are arranged in the door member, and when the door member is closed, the rollers are arranged in the fixing unit. It has a positioning part which positions the roller arranged in the door member to the roller which is.

  In the present invention, at least one roller constituting the reverse conveyance roller pair and at least one roller constituting the conveyance roller pair are arranged in the fixing unit. Therefore, since it is possible to prevent a shift in alignment between the reverse conveying roller pair and the conveying roller pair with a simple configuration, it is possible to prevent the skew of the sheet when the sheet is reversed.

  In addition, by positioning the roller held by the door member of the pair of conveying rollers with respect to the roller provided in the fixing unit, the skewing of the sheet can be prevented with a simple configuration and at low cost. be able to.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an electrophotographic monochrome image forming apparatus which is an example of an image forming apparatus according to a first embodiment of the present invention.

  In FIG. 1, reference numeral 1 denotes a monochrome image forming apparatus, and 1A denotes a monochrome image forming apparatus main body (hereinafter referred to as an apparatus main body). The apparatus main body 1A is provided with an image forming unit 2 for forming a toner image. The image forming unit 2 includes a photosensitive drum 3 and a developing device (not shown) including a developer (toner). A laser scanner 4 that exposes a laser corresponding to the image information from an image data input unit (not shown) is installed on the side of the image forming unit 2.

  In such an image forming unit 2, the latent image formed on the surface of the photosensitive drum 3 by the laser exposure from the laser scanner 4 is developed using a developing material by a developing device (not shown), whereby the photosensitive drum 3. A toner image is formed on the surface.

  Reference numeral 10 denotes a sheet feeding cassette which is a sheet stacking unit provided in the lower part of the apparatus main body 1A. Reference numeral 16 denotes a transfer unit which transfers a toner image formed on the photosensitive drum 3 to the sheet S. Reference numeral 20 denotes a fixing unit that constitutes a fixing unit including a fixing unit 21 including a pressure roller 21a and a fixing sleeve 21b, which are fixing members for fixing the toner image formed on the sheet S by the transfer unit 16. The fixing unit 20 is attachable to and detachable from the apparatus main body 1A in a substantially horizontal direction and in a direction substantially perpendicular to the sheet conveying direction.

  A sheet discharge tray 30 is a sheet stacking means provided on the upper surface of the apparatus main body 1A, and 41 is a double-sided conveyance path. When image formation is performed on the back surface (second surface) of the sheet S, one side (first surface) The sheet S after image formation on one side) is conveyed to the double-sided conveyance path 41. Reference numeral 25 denotes a double-sided conveyance roller pair provided in the double-sided conveyance path 41. The double-sided conveyance roller pair 25 includes a double-sided conveyance roller 25a and a double-sided conveyance roller 25b.

  Reference numeral 5 denotes a sheet reversing unit, 22 denotes a double-sided reversing flapper that is provided in the sheet reversing unit 5 and changes the conveyance path, and 24 denotes a reversing roller pair 24 that can be rotated forward and backward. When performing double-sided printing in which images are formed on both sides of the sheet, the sheet S on which the toner image is fixed on one side by the fixing unit 21 is conveyed to the pair of reverse rollers 24 by switching the double-sided reverse flapper 22. The paper is conveyed to the double-sided conveyance path 41 by reversing the reversing roller pair 24.

  Next, an image forming operation in the monochrome image forming apparatus 1 configured as described above will be described.

  When the image forming operation is started, a predetermined number of sheets S stacked in the sheet feeding cassette 10 are separated and sent out one by one by the feeding roller 11 and the separation roller 12. Then, the sheet S sent out by the feeding roller 11 is conveyed to the registration roller pair 15, and the skew feeding is corrected by the registration roller pair 15.

  Next, the sheet S whose skew has been corrected is then sequentially conveyed by the registration roller pair 15 to the transfer unit 16 that transfers the toner image formed on the surface of the photosensitive drum onto the sheet. The toner image is transferred. Next, the sheet S to which the toner image has been transferred is pressurized and heated by a pressure roller 21a and a fixing sleeve 21b constituting the fixing unit 21 to fix the toner image, and then passes through the sheet conveyance path 31. The paper is discharged to the paper discharge tray 30 by the paper discharge roller pair 23.

  On the other hand, during double-sided printing, a double-sided inversion flapper 22 is moved from a position indicated by a solid line to a position indicated by a broken line as shown in FIG. The fixed sheet S is conveyed to the reverse roller pair 24. Then, the reverse roller pair 24 is reversed before the entire sheet is conveyed to the paper discharge tray 30 after the sheet trailing edge has passed through the duplex reversing flapper 22, whereby the sheet S has the trailing edge as the leading edge. It is conveyed to 41.

  The sheet S conveyed to the double-sided conveyance path 41 is provided on the double-sided conveyance path 41 and is a double-sided conveyance that is a pair of conveyance rollers that conveys the sheet S that is reversed and conveyed by the reverse roller pair 24 toward the image forming unit 2. The paper is conveyed to the refeed roller pair 14 by the roller pair 25. Then, the sheet S conveyed by the re-feed roller pair 14 merges with a conveyance path conveyed by the sheet feed roller 11, and then conveyed to the transfer unit 16 via the registration roller pair 15, and thus on the back surface. The toner image is transferred.

  Next, the toner image transferred to the back surface of the sheet S is fixed by the fixing unit 21, and then the sheet S is conveyed to the opposite side of the discharge roller by switching to the position indicated by the solid line of the double-sided reverse flapper 22. The paper is discharged onto the tray 30 to complete double-sided printing.

  By the way, in FIG.1 and FIG.2, 40 is a door unit provided in the side surface of the apparatus main body 1A, and this door unit 40 can be opened and closed in the arrow direction. The door-side guide member 42 provided on the door unit 40 and the fixing-unit-side guide member 29 provided on the fixing unit side form a double-sided conveyance path 41 that is a re-conveyance path. In the present embodiment, as shown in FIG. 2, the sheet conveyance path 31 and the reverse roller pair 24 that is the reverse conveyance roller are arranged in the fixing unit.

  FIG. 3 shows a state of the upper part of the apparatus main body when the door unit 40 is opened, and FIG. 4 shows a state of the upper part of the apparatus main body when the door unit 40 is closed.

  Here, as shown in FIG. 3, the double-sided conveyance roller (roller) 25a constituting the double-sided conveyance roller pair 25 is provided (arranged) on the fixing unit (apparatus body) side, and the double-sided conveyance roller 25b is a door unit. 40 is provided (arranged). That is, the double-sided conveyance roller 25a and the double-sided conveyance roller 25b constituting the double-sided conveyance roller pair 25 can be separated as the door unit 40 is opened and closed.

  The double-sided conveyance roller 25b provided in the door unit 40 is rotatably held at both ends by a positioning member 26 that is a holding member. The positioning member 26 is held in a slide space 40 a formed in the door unit 40 so as to be slidable on the fixing unit side with play in the vertical direction, and protrudes toward the fixing unit side by a pressing spring 27. It is like that.

  With this configuration, the positioning member 26 can move in the vertical direction when the door unit 40 that is a door member is opened. Since the positioning member 26 can be moved in the vertical direction in this way, when the door unit 40 is closed as will be described later, the double-sided conveyance roller 25b contacts the double-sided conveyance roller 25a while moving the positioning member 26. It can be moved to a contact position. A receiving recess 26 a is formed at the tip of the positioning member 26.

  On the other hand, a double-sided conveyance roller 25a provided in the fixing unit 20 can be rotated by a shaft (not shown), and positioning protrusions 28 are provided on both sides of the double-sided conveyance roller 25a.

  When the door unit 40 is closed, the receiving recess 26a formed on the positioning member 26 and the positioning projection 28 on the fixing unit 20 side are fitted as shown in FIG. Positioning is performed in contact with the double-sided conveyance roller 25a. In other words, in the present embodiment, when the door unit 40 is closed by the positioning member 26 that is the fitting portion and the positioning projection portion 28 that is the fitted portion, the roller on the door unit side (door member side) A positioning unit for positioning a certain duplex conveying roller 25b is configured.

  Since the positioning member 26 is movably held by the door unit 40, the positioning member 26 moves while being moved even when the positioning projection 28 is displaced when being fitted to the positioning projection 28. The positioning projection 28 is fitted. As a result, the positioning member 26 can be securely fitted to the positioning projection 28.

  Here, when the positioning member 26 and the positioning protrusion 28 are fitted in this manner, the double-sided conveyance roller 25b and the double-sided conveyance roller 25a are configured such that the axial centers are at the same height. Thereby, when the positioning member 26 is fitted to the positioning projection 28 by closing the door unit 40, the position of the double-sided conveyance roller 25b with respect to the double-sided conveyance roller 25a is determined.

  When the door unit 40 is closed in this manner, the position of the duplex conveyance roller pair 25 is determined by the fixing unit 20 by determining the position of the duplex conveyance roller 25b with respect to the duplex conveyance roller 25a. Further, the position of the door unit 40 relative to the apparatus main body 1A is determined by positioning means (not shown).

  Note that the door unit 40 is opened to process a jammed sheet, for example. When the door unit 40 is thus opened, the door side guide member 42 moves together with the door unit 40, and the double-sided conveyance path 41 is opened accordingly. Further, the double-sided conveyance roller 25b also moves together with the door unit 40 and is separated from the double-sided conveyance roller 25a.

  When the door unit 40 is thus opened, the double-sided conveyance path 41 is opened, thereby improving the visibility of the jam sheet in the double-sided conveyance path 41 and separating the double-sided conveyance roller 25b from the double-sided conveyance roller 25a. Therefore, the jam processing can be easily performed.

  Incidentally, as described above, the position of the duplex conveying roller pair 25 is determined by the fixing unit 20, and the fixing unit 21 and the reverse roller pair 24 are provided in the fixing unit 20 as described above. In other words, in the present embodiment, the positions of the fixing unit 21, the reverse roller pair 24, and the duplex conveying roller pair 25 are determined in the fixing unit 20.

  The fixing unit 21, the reversing roller pair 24, and the duplex conveying roller pair 25 are configured so that the positions of the fixing unit 21, the reversing roller pair 24, and the duplex conveying roller pair 25 are determined in the fixing unit. The accuracy of the positional relationship of the pair 25 can be improved. That is, misalignment of the fixing unit 21, the reversing roller pair 24, and the double-sided conveyance roller pair 25 can be reduced.

  As a result, it is possible to reduce skew caused by misalignment between the fixing unit 21 and the reverse roller pair 24 before the sheet reversal and between the reverse roller pair 24 and the double-sided conveyance roller pair 25 after the sheet reversal.

  Thus, in the present embodiment, when the door unit 40 is closed, the positioning unit can position the double-sided conveyance roller 25b with respect to the double-sided conveyance roller 25a arranged in the fixing unit 20. In other words, the positioning of the double-sided conveyance roller 25b on the door unit side (roller holding member side), which is a roller other than the rollers provided in the fixing unit 20, disposed in the door unit 40, is fixed through the positioning unit. This can be done by the unit 20.

  As a result, it is possible to reduce misalignment in the alignment between the fixing unit 21, the duplex conveying roller pair 25, and the reverse roller pair 24, and it is possible to skew the sheet S in the duplex conveying path 41 with a simple configuration and low cost. Can be prevented.

  As shown in FIG. 2, the sheet conveyance path 31 that guides the fixing unit 21 from the transfer unit to the paper discharge roller pair 23 or the reverse roller pair 24 is provided in the fixing unit 20 as described above. Further, as described above, the position of the door-side guide member 42 that forms the double-sided conveyance path 41 together with the fixing unit-side guide member 29 is determined by the fixing unit 20. As a result, the position can be determined with high accuracy also in the sheet conveyance path 31 and the double-sided conveyance path 41, and as a result, the skew feeding of the sheet can be reduced and conveyed.

  Next, a second embodiment of the present invention will be described.

  FIG. 5 is a diagram illustrating a state of the fixing unit and the duplex conveying roller pair in a state in which the door unit of the image forming apparatus according to the present embodiment is opened, and FIG. 6 is a diagram illustrating a state in which the door unit is closed. 5 and 6, the same reference numerals as those in FIGS. 3 and 4 described above indicate the same or corresponding parts.

  In FIGS. 5 and 6, reference numeral 43 denotes a support part protruding from the door unit 40, and the double-sided conveyance roller 25 b is rotatably supported (held) by the support part 43. Further, a positioning projection 43a, which is a fitting portion, is provided on the side surface of the support portion 43.

  Reference numeral 44 denotes a positioning member which is a fitted portion provided on the fixing unit side, and the positioning member 44 is fitted with a positioning projection 43a protruding from the support portion 43 of the door unit 40. A joint hole 44a is formed.

  When the door unit 40 is closed, as shown in FIG. 6, the positioning protrusion 43 a protruding from the support portion 43 is fitted into the fitting hole 44 a of the positioning member 44. It contacts the double-sided conveyance roller 25a. Here, when the positioning protrusion 43a is fitted in the fitting hole 44a in this way, the axial centers of the double-sided conveyance roller 25b and the double-sided conveyance roller 25a are configured to have the same height position.

  Thereby, when the door unit 40 is closed, the position of the double-sided conveyance roller 25b with the double-sided conveyance roller 25a is determined. That is, the position of the duplex conveying roller pair 25 is determined by the fixing unit 20. That is, in the present embodiment, the positioning projection 43a and the positioning member 44 constitute a positioning unit that positions the double-sided conveyance roller 25b when the door unit 40 is closed.

  As described above, also in this embodiment, the position of the fixing unit 21, the reverse roller pair 24, and the duplex conveying roller pair 25 is determined in the fixing unit 20 as in the first embodiment described above. Yes. As a result, the misalignment of the fixing unit 21, the reversing roller pair 24, and the duplex conveying roller pair 25 can be reduced, and the skew caused by the misalignment can be reduced.

  Next, a third embodiment of the present invention will be described.

  FIG. 7 is a diagram showing a configuration of an electrophotographic monochrome image forming apparatus which is an example of the image forming apparatus according to the present embodiment. In FIG. 7, the same reference numerals as those in FIG. 1 described above indicate the same or corresponding parts.

  In FIG. 7, reference numeral 50 denotes a document reading device provided in the upper part of the apparatus main body. Here, in the present embodiment, the fixing unit 20 is detachably provided on the apparatus main body 1A. When the fixing unit 20 is taken out, the fixing unit 20 is pulled out.

  Note that when the document reading device 50 or the like is disposed above the fixing unit 20 as in the present embodiment, when the fixing unit 20 is configured to be pulled out in the height direction, the document reading device 50 may interfere. Since the work space is small, the replacement is difficult.

  For this reason, in the present embodiment, as shown in FIG. 8, the fixing unit 20 is configured to be pulled out in a substantially horizontal direction (substantially in the direction of the arrow) with respect to the sheet conveying direction. The fixing unit 20 may be configured to be detachable in a substantially horizontal direction and in a direction substantially parallel to the sheet width direction.

  Incidentally, also in the present embodiment, the fixing means 21, the reversing roller pair 24, and the double-sided conveying roller 25a are provided in the fixing unit 20, and the fixing unit 20 is a main body that is a frame body (not shown) of the apparatus main body 1A. It is configured to be positioned directly on the frame. Then, by directly positioning the fixing unit 20 on the main body frame in this way, the fixing unit 20 can be accurately positioned on the apparatus main body 1A.

  As a result, the misalignment between the double-sided conveyance roller pair 25 and the re-feed roller pair 14 provided in the apparatus main body 1A is reduced. Can also be reduced.

  In the above description, the case where the reverse roller pair 24 is attached to the fixing unit 20 has been described. However, one of the reverse roller pair 24 may be provided in the door unit 40 in the same manner as the double-sided conveyance roller 25b. good. That is, at least one roller constituting the reverse conveying roller pair 24 and at least one roller constituting the double-sided conveying roller pair 25 may be provided in the fixing unit 20, and another roller may be provided in the door unit 40. .

1 is a diagram showing a configuration of an electrophotographic monochrome image forming apparatus which is an example of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of a sheet reversing unit provided in the monochrome image forming apparatus. The figure which shows the state of the apparatus main body when the door unit in the said monochrome image forming apparatus is open | released. The figure which shows the state of the apparatus main body when a door unit in the said monochrome image forming apparatus is closed. The figure which shows a state when the door unit in the monochrome image forming apparatus which concerns on the 2nd Embodiment of this invention is open | released. The figure which shows a state when the door unit in the said monochrome image forming apparatus is closed. FIG. 6 is a diagram illustrating a configuration of an electrophotographic monochrome image forming apparatus that is an example of an image forming apparatus according to a third embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration for attaching and detaching a fixing unit in the monochrome image forming apparatus. 1 is a diagram illustrating a configuration of a conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Monochrome image forming apparatus 1A Monochrome image forming apparatus main body 2 Image forming part 14 Refeed roller pair 20 Fixing unit 21 Fixing means 21a Pressure roller 21b Fixing sleeve 24 Reversing roller pair 25 Double-sided conveyance roller pair 25a Double-sided conveyance roller 25b Both-sided conveyance Roller 26 Positioning member 26a Receiving recess 28 Positioning protrusion 31 Sheet conveying path 40 Door unit 41 Double-sided conveying path 43 Supporting part 43a Positioning protrusion 44 Positioning member 44a Fitting hole 50 Document reading device S Sheet

Claims (5)

An image forming unit that forms a toner image; a fixing unit that includes a fixing member that fixes the toner image transferred to the sheet to the sheet; and a sheet on which the toner image is fixed is transported to the image forming unit again. A re-conveying path, a reversible conveying roller pair capable of reversing the sheet on which the toner image is fixed and conveyed to the re-conveying path, and a reversing conveyance roller pair provided in the re-conveying path and reversed by the reversing conveying roller pair. A pair of conveying rollers that convey the sheet conveyed to the image forming unit,
The fixing unit is detachably provided in an image forming apparatus main body, and at least one roller constituting the reverse conveying roller pair and at least one roller constituting the conveying roller pair are arranged in the fixing unit. Image forming apparatus. An image forming unit that forms a toner image; a fixing unit that includes a fixing member that fixes the toner image transferred to the sheet to the sheet; and a sheet on which the toner image is fixed is transported to the image forming unit again. A re-conveying path, a pair of reversing conveying rollers capable of reversing forward and reversing the sheet on which the toner image is fixed and conveying the sheet to the re-conveying path, and the re-conveying path. In the image forming apparatus comprising a pair of conveying rollers that convey the sheet conveyed in the direction toward the image forming unit, and a door member that forms the re-conveying path and that can be opened and closed in the image forming apparatus main body.
Arranging at least one roller constituting the reverse conveying roller pair and at least one roller constituting the conveying roller pair in the fixing unit;
A roller other than the rollers arranged in the fixing unit among the rollers constituting the reverse conveying roller pair and the conveying roller pair is arranged on the door member,
An image forming apparatus comprising: a positioning unit that positions the roller disposed on the door member with respect to the roller disposed on the fixing unit when the door member is closed.   The positioning portion includes a fitting portion formed on a holding member that holds the roller on the door member side, and a fitted portion that is formed on the fixing portion and is fitted to the fitting portion. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 3, wherein when fitting with the fitted portion, the fitting portion is held movably on the door member so as to be fitted with the fitted portion while moving. apparatus.   The image forming apparatus according to claim 2, wherein the fixing unit is detachably provided on the main body of the image forming apparatus.

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