JP5672996B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus capable of forming an image on both sides of a recording medium (hereinafter referred to as “sheet”). More specifically, the present invention is arranged to face an image forming unit that forms an image on a sheet. The present invention relates to an image forming apparatus including a conveying belt for conveying and capable of forming an image on both sides of a sheet.

In an image forming apparatus having a conveying belt for conveying a sheet and capable of forming an image on both sides of the sheet, the recording material (sheet) is returned at the time of double-sided recording (double-sided image formation) for the purpose of suppressing the increase in size and cost of the apparatus. An image forming apparatus having a configuration in which a return portion that moves in a direction opposite to the normal conveyance direction of the recording material of the conveyance belt is disposed in a part of the conveyance path, and the recording material is returned and conveyed in this portion is already known (for example, , See Patent Document 1).
According to the invention described in Patent Document 1, it is not necessary to provide another return conveyance path, and it is possible to eliminate the installation space when another return conveyance path is provided and a conveyance member required for conveying the recording material in that portion. It is possible to suppress an increase in size and cost.

  Patent Document 1 discloses a configuration in which the return portion is provided in a substantially linear shape, and the recording material circulates from the exit of the return portion in the moving direction through a detour path different from the conveyance belt. According to the configuration described in Patent Document 1, by providing a detour path, a detour path with a small curvature becomes possible, and it becomes possible to suppress the occurrence of wrinkles on the recording material to be conveyed back. is there.

An image forming apparatus that includes a conveyance belt that conveys a sheet and can form an image on both sides of the sheet, and a duplex unit that reverses the sheet for printing the second side of the sheet on which the first side is printed (image formation); , A conveying device provided with an adsorption belt (conveying belt) that adsorbs and conveys paper by electric charge, and a charging device that charges the electric charge to the conveying device. An image forming apparatus configured to adjust the conveyance timing of a sheet conveyed from a unit is already known (see, for example, Patent Document 2).
According to the invention described in Patent Document 2, the charging start position for charging the transport device and the position where the sheet transported from the duplex unit for printing the second surface comes into contact with the transport device are matched. An image forming apparatus capable of transporting a sheet of paper can be provided, and a charging start position and a position at which the sheet transported from the duplex unit for printing the second surface comes into contact with the transport apparatus. It is possible to provide a mechanism having a simple configuration.

  However, both the image forming apparatuses described in Patent Documents 1 and 2 described above are both surfaces that adopt a return conveyance path to a part of the conventional conveyance belt and circulate through a detour path (reversal path) different from the conveyance belt. In the transport apparatus configuration, the shape and configuration of the detour path are not taken into consideration. In particular, the detour path includes at least two locations and parts that have an R shape with a curved movement trajectory of the sheet, and includes transport means (including transport means such as a pair of transport rollers and auxiliary transport means). In the case of a detour route that is not, the following problems occur due to the difference in the R shape location / part in the detour route and the relative size of the R shape (hereinafter also referred to as “R shape / configuration”). It is necessary to fully consider the R shape and configuration of the route.

In other words, depending on the R shape and configuration of the detour route,
(1) Paper load fluctuations occur in the detour path, which adversely affects paper feed accuracy and images.
(2) Even if the load fluctuation of the paper on the detour path is large, immediately after the detour path, a transport means having a transport force capable of canceling the influence of the load fluctuation in the detour path more than the load of the detour path is provided. Can cancel the influence of the load on the detour path, but the influence when the trailing edge of the sheet passes the load immediately after the detour path deteriorates the sheet feeding accuracy and image.

In order to simplify the explanation, the problem (1) is that the curved R shape (sheet movement locus) on the most downstream side in the paper conveyance direction in the detour path is the R2 shape, When the R-shaped portion is the R1 shape and the R2 shape is smaller than the R1 shape (R2 <R1), it can be explained as follows. That is, when a sheet on which a single-sided image is formed is held at a position facing the image forming unit (particularly, facing the ink jet recording head and sucked and held by the conveyance belt), the sheet is conveyed most downstream in the sheet conveyance direction. When the R2 shape on the side is smaller than the R1 shape on the upstream side in the sheet conveying direction, the sheet moves from the R1 shape portion having a relatively small load to the R2 shape portion having a large load, so that the rear end portion of the sheet has a large load. Since there is no load that cancels out the influence of the load fluctuation (load fluctuation of the R2 shape portion) when exiting the R2 shape portion of the sheet, the load variation affects the sheet at the position directly opposite to the image forming unit. A paper feeding accuracy defect occurs due to overfeeding (overfeeding) than the initial transport distance (which is set at a position facing and holding the forming unit). As a result, the image forming position in the image forming unit is shifted (in the ink jet method, the ink landing position is shifted in the recording head), and the image position accuracy is deteriorated. The details of (1) and (2) will be described more specifically in comparative examples in the embodiments described later.
From the above, it is possible to suppress the paper feeding accuracy and the influence on the image only by providing a simple bypass path shape and configuration (a shape and configuration that is symmetrical when viewed from the side of the machine). There is no problem.

  Further, in the image forming apparatus described in Patent Document 2, a sheet on which a single-sided image has been formed at the most upstream portion of the curved portion R in the second path B (reversing path). Since the image forming surface side of the sheet is always directed outward, there is a problem that the image forming surface of the sheet is rubbed against the guide surface at the R-shaped portion of the reversing path. That is, the image forming apparatus described in Patent Document 2 has a problem of causing problems such as paper contamination and wear of the R-shaped portion of the reverse path.

  The present invention has been made in view of the above-described problems and circumstances. In an image forming apparatus that includes a conveyance belt that conveys a sheet and can form an image on both sides of the sheet, an R-shaped portion of a reversing path including a bypass path An object of the present invention is to realize and provide an image forming apparatus capable of suppressing the sheet feeding accuracy and the influence on the image by optimizing the shape and configuration of the image forming apparatus.

In order to solve the above-described problems and achieve the above-mentioned object, the invention according to each claim employs the following characteristic means / invention-specific matters (hereinafter referred to as “configuration”).
According to the first aspect of the present invention, there is provided a conveying belt that is wound around at least two rotating members and is circulated and arranged so as to be opposed to the conveying belt, and is conveyed by the conveying belt. An image forming unit that forms an image on the sheet, a refeed unit that switches back the sheet on which the one-sided image is formed that has passed through the conveying belt, and re-feeds the sheet again to the image forming unit side, and the re-feed In the image forming apparatus having a reversing path for reversing the front and back of the sheet on which the single-sided image is formed fed by the means and guiding the sheet to the opposite conveying belt surface facing the image forming means again, The reversing path includes at least two locations where the movement trajectory of the sheet guided by the reversing path has a curved R shape, and is located on the most downstream side in the sheet conveyance direction in the reversing path. The R shape is configured to be larger than other R shapes upstream in the sheet conveyance direction, and the guide surface at the most upstream R shape in the sheet conveyance direction is an image of a sheet on which a single-sided image has been formed. The forming surface side is configured to be curved inward along the sheet conveying direction .

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the refeeding unit refeeds the sheet on which the single-sided image has been formed on the conveying belt surface on the opposite side that does not face the image forming unit. The reversing path is configured to face the image forming unit in the moving direction of the conveying belt after a sheet on which a single-sided image has been formed passes the conveying belt surface on the opposite side. It is a detour route that detours around the outer periphery of the conveyor belt that is wound around the rotating member upstream of the section and guides it to the opposite conveyor belt surface.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the distance of the reversing path is set to be equal to or less than a sheet length in the sheet conveying direction in a minimum sheet size usable in the image forming apparatus. It is characterized by.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the reversing path does not include a conveying unit.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the image forming apparatus includes a sheet storage unit that is detachable from the main body of the image forming apparatus and stores the sheet. The reversing path is disposed at a position retracted from the insertion / removal region of the sheet storage means.

According to the present invention, a novel image forming apparatus can be realized and provided by solving the above-described problems. The effects for each claim are as follows.
According to the first aspect of the present invention, the configuration can suppress the sheet feeding accuracy and the influence on the image at the time of double-sided image formation, and is relatively small on the most upstream side in the sheet conveyance direction in the reversing path. Image rubbing with respect to the guide surface at the R-shaped portion can also be suppressed.

According to the second aspect of the present invention, it is possible to suppress an increase in size and cost of the apparatus by the configuration.
According to the third aspect of the present invention, with the above configuration, the apparatus size (machine size) can be reduced to the minimum necessary, and a roller or the like for conveying the sheet in the reversing path (including the detour path) can be provided. The conveying means can also be removed, and cost increase can be suppressed.

According to the fourth aspect of the present invention, the above-described configuration can eliminate the influence of printing misalignment (particularly in the case of a small size sheet) and sheet trailing edge omission due to the difference in linear velocity of the sheet.
According to the fifth aspect of the present invention, the device can further reduce the size of the apparatus (downsizing) by the above configuration.

1 is a simplified front view of an entire inkjet printer showing a first embodiment of the present invention. (A), (B), (C) is a figure explaining the relationship between the structure of various detours, and a load fluctuation | variation. It is a figure explaining the influence in the load in the detour of this invention of FIG. 2 (B), paper feed precision, and an image. It is a figure explaining the influence in the load in the detour of the comparative example 2 of FIG.2 (C), paper feed precision, and an image. It is a figure explaining the influence in the load in the detour of this invention of FIG. 2 (B), paper feed precision, and an image. It is a simplified front view of the whole inkjet printer which shows the 2nd Embodiment of this invention. (A), (B) is explanatory drawing explaining the modification 1 of 1st thru | or 2nd embodiment. It is a figure which shows an example of a structure and shape of a detour different from the modification 1. FIG. 10 is a simplified front view illustrating a main configuration of an inkjet printer according to a second modification.

  Hereinafter, embodiments of the present invention including examples will be described in detail with reference to the drawings. In each embodiment and each modification, etc., components (members, components, etc.) having the same function, shape, etc. will be described by giving the same reference numerals after having been described once unless there is a possibility of confusion. Is omitted. In order to simplify the drawings and the description, even if the components are to be represented in the drawings, the components that do not need to be specifically described in the drawings may be omitted as appropriate. When quoting and explaining constituent elements such as published patent gazettes, the reference numerals are shown in parentheses to distinguish them from those of the embodiments.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a simplified front view of the entire ink jet printer showing the first embodiment of the present invention.

First, with reference to FIG. 1, a configuration of an entire inkjet printer that is an inkjet recording apparatus as an example of an image forming apparatus according to a first embodiment of the present invention will be described. An inkjet printer 100 shown in the figure is a serial type inkjet printer that forms an image by an inkjet method.
The ink jet printer 100 includes an image forming unit 50 including a recording head 3 as an image forming unit that forms an image by an ink jet method, and a transport unit 51 including a transport belt 10 that transports a sheet 9 as an example of a sheet. A paper feeding unit 52 that feeds and feeds paper 9, a paper discharge unit that discharges and discharges paper on which image formation (hereinafter also referred to as “printing”), and a single-side printed paper are switched back. A paper discharge reversing unit 53 that re-feeds the paper to be reversed.

  As the sheet conveyance path, the sheet 9 fed from the sheet feeding unit 52 is connected to and communicated with the sheet feeding conveyance path 55, which is a path for conveying the sheet 9 to the conveyance unit 51, and the front surface (first The image forming unit is used to form a single-sided printed sheet on which an image is formed on the first side) and a double-sided printed sheet on which the single-sided printed sheet has been switched back and reversed to form an image on the remaining back side (second side). 50 is connected to and communicated with the common conveyance path 56, which is a path for conveying downstream of the sheet 50, and is switched back and re-fed by a pair of discharge rollers 11 and 12 (to be described later) constituting a re-feeding unit. Refeeding as a refeeding path for guiding the one-side printed paper to the surface of the conveying belt 10 on the opposite side that does not face the recording head 3 of the image forming unit 50 (hereinafter referred to as “anti-opposing surface 10a”). Road 57 and single-sided printed paper are carried After passing through the opposite surface 10 a of the belt 10, it bypasses the outer periphery of the conveyance belt 10 that is wound around the conveyance roller 1 on the upstream side of the portion facing the recording head 3 in the moving direction of the conveyance belt 10. A detour 6 serving as a reversing path for guiding the reversed one-side printed paper to the surface of the conveying belt 10 facing the recording head 3 again (hereinafter referred to as “opposing surface 10a”) is provided. The detour route 6 which is also an inversion path will be described in detail later because it includes the characteristic configuration of the present invention.

  The paper feed conveyance path 55 is formed by a guide member 55 a and a guide member 6 a outside the bypass 6. The common conveyance path 56 is formed by a pair of guide members 56a, 56b and the like. The refeed path 57 is formed by a pair of guide members 57a, 57b and the like. The detour 6 is formed by an outer guide member 6a and an inner guide member 6b.

  The image forming unit 50 includes a carriage 3A (indicated by a broken line in the figure) that can be scanned and moved. The carriage 3A is driven by a master-slave guide rod (not shown), which is a guide member installed horizontally and fixed on the main body of the apparatus, in the main scanning direction (the front side and the back side of the page perpendicular to the page). Direction). The carriage 3A is connected to a main scanning motor (not shown) via a timing belt (not shown), and is reciprocated and scanned in the main scanning direction by the main scanning motor. The carriage 3A is shown and described only in the present embodiment, and is omitted in the following embodiments and the like for the sake of simplicity of the drawings and description.

On the carriage 3A, a recording head 3 including a liquid discharge head for discharging ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K) is mounted. The recording head 3 is disposed to face the conveying belt 10 and functions as an image forming unit or a recording unit that forms an image on the sheet 9 conveyed by the conveying belt 10. The recording head 3 has a nozzle row composed of a plurality of nozzles arranged in the sub-scanning direction Xa (also the sheet conveying direction Xa) orthogonal to the main scanning direction, and is mounted with the ink droplet ejection direction of the nozzles oriented vertically. Yes.
The recording head 3 has, for example, four nozzle rows and ejects black (K), cyan (C), magenta (M), and yellow (Y) droplets.

  The carriage 3 </ b> A is mounted with a head tank (not shown) for supplying ink of each color corresponding to the nozzle row of the recording head 3. The head tank is replenished and supplied with the recording liquid of each color via a supply tube of each color by a supply pump unit (not shown) from the recording liquid cartridge of each color that is detachably mounted in a cartridge loading section (not shown). It has become so.

The paper feed unit 52 is configured to cooperate with the paper feed roller 17 and the paper feed roller 17 that feeds the paper 9 on the paper feed tray 8. And a separation pad 18 for separating and feeding them one by one.
A separation pad 18 made of a material having a large coefficient of friction is provided opposite to a sheet feeding roller 17 that separates and feeds a plurality of sheets 9 stacked on the sheet feeding tray 8 one by one. The roller 17 is biased. The paper feed tray 8, the paper feed roller 17, and the separation pad 18 constitute a paper feed unit.

  A transport unit 51 is arranged to feed the sheet 9 fed from the sheet feeding unit 52 during single-sided printing and the single-sided printed sheet 9 reversed during double-sided printing to a position facing the recording head 3 of the image forming unit 50. Has been. The conveyance unit 51 includes a conveyance belt 10, a conveyance roller 1, a tension roller 2, a tip roller 4, a charging roller 7, a conveyance guide plate 20, a separation claw 13, and the like.

  The transport belt 10 is for electrostatically attracting the fed paper 9 and transporting it to a position facing the recording head 3, and serves as a transport means for intermittently transporting the paper 9 in the sheet transport direction Xa. Function. The conveying belt 10 is an endless belt, and is wound around and wound between a conveying roller 1 as a driving / rotating member and a tension roller 2 as a driven / rotating member, and the belt moving direction Xa (sheet conveying) And the sub-scanning direction Xa).

The conveyance roller 1 is rotationally driven by a drive system including a driving unit such as a sub-scanning motor (not shown) via a timing belt (not shown) as a driving force transmission unit. The conveyance belt 10 rotates in the belt movement direction Xa indicated by the arrow when the conveyance roller 1 is rotationally driven by the sub scanning motor (not shown).
The conveyance belt 10 of the present embodiment is an endless belt, but may be an endless belt in molding or an endless belt by connecting both ends.

  The conveyor belt 10 has a single-layer or multi-layer structure, and at least a side (surface layer) in contact with a sheet and a charging roller 7 described later (surface layer) is made of a resin such as PET, PEI, PVDF, PC, ETFE, or PTFE, or an elastomer. It has an insulating layer formed of a material that does not contain a conductive control material, and holds electric charges. In addition, when it is set as the structure of two or more layers, it can be set as the structure which has the electroconductive layer which made the said resin or elastomer contain carbon in the side which does not contact the charging roller 7. FIG.

The leading end roller 4 functions as a pressing member that presses the transport belt 10 from the front surface side (transport surface side). The leading end roller 4 is disposed in the vicinity of the upstream side of the recording head 3 in the belt movement direction Xa of the conveying belt 10 so as to press the conveying roller 1 via the conveying belt 10, and the sheet 9 is in close contact with the conveying belt 10. Let
The conveyance guide plate 20 is disposed between the conveyance roller 1 and the tension roller 2 at a position facing the recording head 3 inside the conveyance belt 10 and serves as a belt guide member that guides the conveyance belt 10 from the inside. Function.
The separation claw 13 is disposed on the downstream side of the recording head 3 in the belt moving direction Xa so as to press against the tension roller 2 via the conveyance belt 10 and functions as a separation member that separates the paper 9 from the conveyance belt 10. .

  The charging roller 7 is disposed on the upstream side in the belt moving direction Xa of the transport roller 1 and functions as a charging unit for charging the surface of the transport belt 10. The charging roller 7 is disposed so as to come into contact with the surface layer (insulating layer) of the transport belt 10 and to rotate following the circumferential movement of the transport belt 10.

  A positive output and a negative output are alternately repeated with respect to the charging roller 7, that is, an alternating voltage is applied by a voltage applying means (not shown), and a charging voltage pattern in which the conveying belt 10 is alternated, that is, a sub-rotation direction. In the scanning direction Xa, plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 9 is fed onto the conveyance belt 10 that is alternately charged with plus and minus, the sheet 9 is electrostatically attracted to the conveyance belt 10, and the sheet 9 is moved in the sub-scanning direction Xa by the circular movement of the conveyance belt 10. It is conveyed to.

  Therefore, by driving the recording head 3 under the control of a control means (not shown) in accordance with the image signal while moving the carriage 3A, ink droplets are ejected onto the stopped paper 9 to record one line. After the sheet 9 is conveyed by the conveying belt 10 by a predetermined amount, the next line is recorded. The recording operation is terminated when a control means (not shown) receives a recording end signal or a signal indicating that the trailing edge of the paper 9 has exited the printing area 10 which is the recording area of the recording head 3.

  Further, as a paper discharge unit for discharging the paper 9 on which the image is formed and recorded by the recording head 3, a discharge unit that feeds the paper 9 separated from the conveying belt 10 by the separation claw 13 into the paper discharge reversing unit 53 and A pair of paper discharge rollers having a function of refeed means is provided. The pair of paper discharge rollers includes a spur roller 12 having a star-shaped cross section, and a paper discharge roller 11 that is in contact with and in contact with the spur roller 12. Downstream of the sheet discharge rollers 11 and 12 in the sheet conveying direction, a sheet discharge guide member (not shown) for guiding the sheet 9 sent by the sheet discharge rollers 11 and 12 and a sheet discharge (not illustrated) for stacking the sheets 9 are provided. And a tray.

  The spur roller 12 is engaged with the surface of the paper 9 facing the recording head 3 on the downstream side of the recording head 3, but the paper 9 is not only ordinary plain paper but also an OHP sheet, card, postcard, When recording on thick paper such as an envelope, it merely assists the feeding of the paper 9, and the paper 9 is caught between the paper discharge roller 11 and the spur roller 12, that is, the spur roller 12 is paper. 9 does not define a gap between the surface of the sheet 9 and the recording head 3.

Next, a configuration related to double-sided printing will be described.
The paper discharge roller 11 and the spur roller 12 are driven by driving means (not shown) so as to be able to perform a switchback operation for inverting the leading edge and the trailing edge of the single-side printed paper 9 and to rotate in both clockwise and counterclockwise directions. It is comprised so that. That is, the paper discharge roller 11 and the spur roller 12 switch back the single-side printed paper 9 that has passed through the opposite surface 10a of the transport belt 10 and feed it again to the recording head 3 side of the image forming unit 50. It functions as a feeding means.

A branch claw 16 as a branch member that can swing around a support shaft is provided for switching back at a branch portion between the common conveyance path 56 and the refeed path 57 of the paper discharge reversing section 53. . As described above, the refeeding unit mainly includes the paper discharge roller pairs 11 and 12, the refeeding path 57, and the branching claw 16.
A guide member 58 for guiding the single-side printed paper 9 to the surface of the conveying belt 10 is disposed on the surface of the conveying belt 10 that is opposite to the recording head 3 and is not opposed to the recording head 3.
In the drawing of the guide member 58, on the left end side and in the vicinity of the entrance of the detour route 6, a double-sided pressure roller 5 as a pressing member disposed so as to press the conveying roller 1 via the conveying belt 10, and the conveying belt 10. A separation claw 14 as a separation member disposed so as to be pressed against the conveying roller 1 via the gap is disposed.

  Based on FIG. 1, the operation of the ink jet printer 100 of the present embodiment will be described. First, the operation at the time of printing on one side (for example, the surface of the paper which is the first surface of the paper 9) will be described. When a power switch (not shown) is turned on and turned on and various key operations (key operations such as the number of prints and enlargement / reduction) of an operation unit (not shown) by the user are finished, the operation of the inkjet printer 100 is not shown. In response to a control command from the control unit, the paper feeding unit 52 is ready to be activated in synchronization with the image forming unit 50 and the conveyance unit 51. In other words, the paper 9 on the paper feed tray 8 is separated and fed by the cooperative action of the paper feed roller 17 and the separation pad 18 and is guided by the guide members 55a and 6a while the leading end roller of the transport section 51 is moved. 4 and the conveying belt 10 are fed.

  At this time, the conveyance belt 10 is rotated in the sub-scanning direction (belt movement direction) Xa by rotating the conveyance roller 1 by the sub scanning motor (not shown). At this time, the charging roller 7 is in contact with the surface layer of the conveyance belt 10 and is rotated by the rotation of the conveyance belt 10, and through alternating voltage application to the charging roller 7 by voltage application means (not shown). The charging roller 7 is alternately charged in a band shape with a predetermined width between plus and minus. The sheet 9 is fed onto the conveyance belt 10 that is alternately charged with plus and minus, the sheet 9 is electrostatically attracted to the conveyance belt 10, and the sheet 9 is conveyed in the sub scanning direction Xa by the circular movement of the conveyance belt 10. Is done. At this time, the conveyance of the sheet 9 is temporarily stopped at the printing position in the recording head 3.

Next, the carriage 3A is driven so as to move in the main scanning direction (front side and back side perpendicular to the paper surface in FIG. 1), and the recording head 3 is driven according to the image signal to stop. Ink droplets are ejected onto the existing paper 9 to print and record one line, and after a predetermined amount of the paper 9 held on the conveyor belt 10 is conveyed, the next line is printed.
Then, the sheet 9 is conveyed by the conveying belt 10 through the rotational driving of the conveying roller 1 again. At this time, the single-side printed sheet 9 (hereinafter simply referred to as “ The sheet 9 ”(also referred to as“ sheet 9 ”) is sent to the sheet discharge reversing unit 53 by a spur roller 12 driven by the sheet discharge roller 11, and further conveyed downstream in the sheet conveyance direction Xa while being guided by a sheet discharge guide member (not shown). .

  The sheet 9 to be conveyed is conveyed downstream in the sheet discharge direction Xb by the rotational drive of the pair of discharge rollers 11 and 12. When the control means (not shown) receives a recording end signal or a signal that the rear end of the paper 9 has exited the printing area 10 which is the recording area of the recording head 3, the recording operation is ended, and the paper 9 is not shown. Paper is ejected and stacked on the paper ejection tray.

Next, the operation during duplex printing will be described.
After the single-sided printing is performed as described above, the leading edge of the single-sided printed paper 9 is guided to the nip portion of the pair of paper discharge rollers 11 and 12, and the trailing edge of the single-sided printed paper 9 is discharged. When passing through the branch of the reversing unit 53, this is detected by a sensor (not shown), whereby the paper discharge roller 11 and the spur roller 12 start to be reversed, and the front end and the rear end of the single-side printed paper 9 are reversed. A switchback operation is performed. At this time, the conveyance path of the sheet 9 printed on one side is switched to the refeed path 57 side by the branching claw 16 occupying the position shown in FIG.
Next, when the front end of the single-side printed paper 9 that has been switched back (the rear end of the paper 9 before switch back) is detected by a sensor (not shown) that detects the switchback operation, the front end of the single-side printed paper 9 Is conveyed to the left in the drawing of the refeed path 57.

Next, the single-side printed paper 9 is conveyed through the refeed path 57 while being attracted to the opposite surface 10 b of the conveyance belt 10 that does not face the recording head 3. The single-side printed paper 9 conveyed while adsorbed to the opposite surface 10 b of the conveyance belt 10 is conveyed while being pressed against the conveyance roller 1 by the double-side pressure roller 5 via the conveyance belt 10, and is separated by the separation claw 14. Separated from the conveyor belt 10. The separated single-side printed paper 9 is conveyed again to the portion facing the recording head 3 by the conveying belt 10 through the leading end roller 4 while being guided by the bypass 6. At this time, in the same manner as described above, it is attracted to the opposed surface 10 a of the conveyor belt 10 and is attracted and conveyed to the print area of the recording head 3.
Here, since the charging roller 7 is installed inside the bypass 6 at the time of reversal, the single-side printed paper 9 is always attracted onto the newly charged transport belt 10. Since the subsequent operations can be easily understood and implemented by those skilled in the art from the operation during single-sided printing, further detailed description of the operation will be omitted.

  According to the present embodiment, in the inkjet printer 100 which is an image forming apparatus capable of duplex printing, the opposite surface 10b of the conveyance belt 10 that does not face the recording head 3 when re-feeding and reversing a single-side printed paper. Since the refeed means (paper discharge roller pairs 11 and 12, refeed path 57, branch claw 16) is configured so as to refeed and guide the image, the conventional image of the same type as described in Patent Document 1 is used. As with the forming apparatus, the apparatus can be reduced in size and cost can be suppressed.

Next, a specific configuration of the detour 6 will be described in detail (claims 1 to 4).
The detour 6 has at least two locations where the movement trajectory of the sheet (sheet) guided to the detour 6 has a curved R shape, and the R on the downstream side of the sheet conveyance direction Xa in the detour 6. The configuration is the largest. This is because, by adopting a configuration in which a portion where the load fluctuation (hereinafter simply referred to as “load fluctuation”) applied to the paper becomes large is brought to the upstream side in the sheet conveyance direction Xa, This is to suppress the influence on the image. Hereinafter, the portion having the R shape is also referred to as “R shape portion” or “R portion”.

  In FIG. 1, there are two places where the movement locus of the paper has an R shape. The radius of curvature of the R portion upstream of the sheet conveyance direction Xa in the detour 6 is R1, and the radius of curvature of the R portion downstream of the sheet conveyance direction Xa is R2. The relationship between R1 and R2 in the detour 6 is configured such that R1 <R2.

The reason why the effect of the present invention occurs will be described in detail with reference to FIGS. FIG. 2 is a diagram for explaining the relationship between the configuration of various detours (conventional comparative examples 1 and 2 and the present invention) and load fluctuations.
FIG. 2 is a graph in which the upper diagram shows the configuration of various detours, and the lower diagram shows load fluctuations in various detours. 2A shows a comparative example 1 in which the configuration of the R portion of the detour 6X is vertically (or left and right) symmetrical, and FIG. 2B shows the configuration of the R portion of the detour 6 on the downstream side in the sheet conveying direction Xa. A configuration example of the present invention in which the R shape (R2) is the largest is shown. FIG. 2C shows a configuration example of the comparative example 2 in which the R configuration of the detour 6Y has the largest R shape (R1) on the upstream side in the sheet conveyance direction Xa. The horizontal axis in the lower diagram of FIG. 2 indicates the distance from the entrance of the detour (position on the detour), and the vertical axis indicates the magnitude of the load at that distance / position. The distance X of the entrance portion of the detour is X = 0, and the exit portion is X = X1. An arrow in the transport roller 1 indicates the rotation direction of the transport roller 1.

In Comparative Example 1 in FIG. 2A, the configuration of the R portion of the detour 6X is vertically (or left and right) symmetrical, and the size (curvature radius) of the R portion is constant, so the sheet passes the detour 6X. The load when transported is constant.
In the present invention (this embodiment) in FIG. 2B, the R shape increases (R1 <R2) as the sheet is conveyed downstream in the sheet conveyance direction Xa in the detour 6 (R1 <R2). The load is large on the upstream side and small on the downstream side.
In Comparative Example 2 in FIG. 2C, the R shape becomes smaller (R1> R2) as the sheet is conveyed downstream in the sheet conveyance direction Xa in the detour 6Y, so the load at that time is upstream. In, it is small and becomes large in the downstream.

FIG. 3 is a diagram for explaining the load, paper feed accuracy, and influence on the image (part 1) in the alternative route 6 of the present invention shown in FIG. In the same figure, taking the bypass configuration of the present invention in FIG. 2B as an example, the load on the bypass route 6 when the load on the bypass route 6 is on the upstream side in the sheet conveying direction Xa, the paper feed accuracy, and the effect on the image ( It is a figure explaining the 1).
In FIG. 3, hatched (a) shows a load when the sheet is conveyed to the R1 portion, which is the R portion on the upstream side of the sheet conveyance direction Xa in the detour 6. Even if a large load is generated in the region (a), the load (B) in the region larger than the region (a) is included in R2 indicated by the satin pattern that is the R portion downstream in the sheet conveying direction Xa. Therefore, the load (a) is canceled by the load (b), and the paper feeding accuracy and the image are not affected.

FIG. 4 is a diagram for explaining the load, paper feed accuracy, and influence on the image (part 2) in the alternative route 6Y of the comparative example 2 of FIG. In the same figure, taking the bypass route configuration of Comparative Example 2 in FIG. 2C as an example, the load on the bypass route when the load on the bypass route 6Y is on the downstream side in the sheet conveying direction Xa, the paper feed accuracy, and the effect on the image It is a figure explaining (the 2).
4A shows a load when the rear end portion of the sheet is conveyed to R2 which is the R portion on the downstream side of the bypass 6Y. In FIG. 3 described above, even if a large load is generated on the upstream side in the sheet conveying direction Xa, there is no influence on the sheet feeding accuracy and the image because the larger load area is provided on the downstream side in the sheet conveying direction Xa. However, since there is nothing in FIG. 4 that cancels the load of the portion (a), the paper feed accuracy and the image are affected by the load of (a).

In the second comparative example of FIG. 4, when the load (conveying force) at the tip roller 4 shown in FIG. 1 is larger than the load of (a), as in the description of FIG. However, when the trailing edge of the sheet passes through the leading end roller 4, the load cannot be canceled, and the influence on the sheet feeding accuracy and the image is further increased.
Therefore, in the present invention, as shown in FIG. 2B, by adopting a configuration in which R2 which is the R shape (R shape of the movement trajectory of the paper) downstream in the sheet conveying direction Xa is maximized, the paper feed accuracy and the image The effect is suppressed.

FIG. 5 is a diagram for explaining the load, paper feed accuracy, and influence on an image (part 3) in the alternative route 6 of FIG. 2B, which is the alternative route configuration of the present invention.
In the detour configuration of the present invention, R2 which is the R shape downstream of the sheet conveying direction Xa is the largest configuration, so the load when the trailing edge of the sheet exits the detour 6 is shown in FIG. As a result, it is possible to reduce the sheet feeding accuracy and the influence on the image. In addition, since the load of (a) is small, the load of (a) can be reduced together with the load on the leading end roller 4 of FIG. 1, and the influence on the paper feeding accuracy and the image can be suppressed.

  On the other hand, (E) of FIG. 5 shows the case of the detour configuration of the comparative example 1 of (A) of FIG. Although the load on the portion (a) in FIG. 5E can be reduced by increasing the size of the R portion (of the radius of curvature), this will increase the machine size and increase the cost. Also become.

In the present embodiment, the distance of the detour 6 is set to be equal to or less than the sheet (sheet) length in the sheet conveyance direction Xa at the minimum sheet (sheet) size that can be used in the ink jet printer 100 (Claim 3). Here, the distance of the detour 6 means the distance (sheet movement distance) from the center of the nip portion of the double-sided pressure roller 5 of FIG. Although the length of the paper varies depending on the type, in the present embodiment, the length is equal to or shorter than the length of the “postcard” in the longitudinal direction.
As described above, by setting the distance of the detour to be equal to or shorter than the paper length (length in the longitudinal direction of the paper), the load can be reduced to the minimum and the paper feeding accuracy can be improved.

This is because if the distance of the detour is greater than or equal to the paper length, rollers or rollers are disposed on the detour, which may cause a new load and cause a print misalignment. Moreover, the cost by the space and member arrangement | positioning for the part will also arise.
Further, if the distance of the detour is too short, the load increases as a whole, and the pressure of the double-sided pressure roller (for example, the double-sided pressure roller 5 shown in FIG. 1) immediately before separating the paper is increased. Because it becomes necessary, problems will occur even if the distance of the detour is too short.

In the present embodiment, the guide surface shape of the guide members 6a and 6b where the paper movement trajectory in the detour 6 is R-shaped includes single-sided printing including the R-shaped portion R1 at the most upstream side in the sheet conveying direction Xa. The image surface of the used paper is curved inward (Claim 1).
As described above, the configuration of the bypass 6 that curves the image surface of the one-side printed paper so as to face the inner wall surface of the guide member 6b inside the guide members 6a and 6b allows the paper type (sheet Regardless of the type, it is possible to minimize the rubbing of the image surface and to suppress image deterioration on the first surface of the paper (the image surface of the paper that has been printed on one side).

In the present embodiment, the bypass 6 has a configuration that does not include a conveying unit such as a pair of conveying rollers for conveying a sheet, or a roller or a roller that is a conveying auxiliary unit for assisting the conveyance of the sheet. (Claim 4).
With the above-described configuration, it is possible to prevent printing misalignment (deterioration of paper feeding accuracy and influence on images) due to a difference in linear velocity with the roller pair on the downstream side in the sheet conveying direction Xa. It is possible to eliminate the influence of the load fluctuation when the nip at the rear end of the sheet comes off.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a simplified front view of the entire inkjet printer showing the second embodiment of the present invention. In the first embodiment shown in FIG. 1, the ink jet printer 100 in the case where the paper transport path is a horizontal transport path has been described. However, a vertical transport path such as the ink jet printer 100A of the second embodiment shown in FIG. Even in this case, the present invention can be applied.

In the inkjet printer 100A of the second embodiment, compared to the inkjet printer 100 of the first embodiment, instead of the horizontal conveyance path, the sheet conveyance path is a vertical conveyance path that is vertically above and below, and The paper cassette 19 is provided below the detour 6.
The paper feed cassette 19 has a function as a sheet storage unit in which a paper feed tray 8 on which a plurality of sheets 9 are stacked can be inserted into and removed from the ink jet printer main body as the image forming apparatus main body. In the drawing, a broken line indicated by reference numeral 21 represents an insertion / removal region of the paper feed cassette 19 with respect to the ink jet printer main body.

If the detour 6 is increased, the load on the entire detour with respect to the sheet 9 is reduced, so that it is possible to suppress the sheet feeding accuracy and the influence on the image. However, in this case, since the insertion / removal area 21 of the paper feed cassette 19 is moved downward, the paper feed cassette 19 is interfered. Although the bypass path 6 can be made larger than that shown in FIG. 6 and the insertion / removal area 21 of the paper feed cassette 19 can be lowered to the lower side of the machine, which is the main body of the ink jet printer, this increases the machine size.
According to the present embodiment, by providing the bypass 6 so as not to be below the insertion / removal area 21 of the paper feed cassette 19, the machine size can be minimized.

(Modification 1)
With reference to FIG. 7, the modification 1 of the 1st thru | or 2nd embodiment is demonstrated. In the first modification, the configuration and shape of the detour path are the opposite surface 10a (the surface facing the recording head 3) that is also the normal conveyance surface of the conveyance belt 10 and the return side or refeed side surface of the conveyance belt 10. It will be described that the present invention can be applied even when the angle θ with a certain opposite surface 10b (the opposite surface not facing the recording head 3) is 360 degrees or less.

An example in which the angle θ is 360 degrees or less is shown in FIGS. 7 (A) and 7 (B). 7A and 7B, the sign Xa1 indicated by the thick arrow indicates the transport direction on the facing surface 10a of the transport belt 10, and the sign Xa2 indicated by the thick arrow indicates the transport direction on the opposite surface 10b of the transport belt 10. Respectively. In FIG. 7B, reference numeral 15 denotes a driven roller that is rotated by the conveying force of the conveying belt 10. In FIGS. 7A and 7B, the transport roller 1 as a driving / rotating member is disposed upstream in the transport direction Xa1. However, the present invention is not limited to this, and the transport roller 1 may be disposed downstream in the transport direction Xa1. Good.
The angle θ represents the angle between the facing surface 10a of the transport belt 10 and the opposite surface 10b of the transport belt 10. FIGS. 7A and 7B are examples of 360 degrees, and the configuration and shape of the detour of the present invention can be applied even below this angle.

FIG. 8 shows an example of the configuration / shape of the detour 6 in the case where the angle θ is 360 degrees or less, which is different from the modification 1 of FIGS. 7 (A) and 7 (B). The detour 6A shown in FIG. 8 has three locations (R1, R2, and R3) where the movement locus of the sheet has an R shape (R1, R2, R3), and R3 on the most downstream side of the detour 6A is the movement locus of the sheet. Is the largest.
Even if the angle θ is 360 degrees or less, the rearmost end portion of the sheet is conveyed to the most downstream side of the detour 6A by setting the most downstream R3 of the detour 6A as shown in FIG. The load at the time of printing can be reduced to the minimum, and the paper feeding accuracy and the influence on the image can be suppressed.

(Modification 2)
Modification 2 will be described with reference to FIG. Modification 2 is an example in which the present invention is applied to an inkjet image forming apparatus disclosed in, for example, FIG. 1 of Patent Document 2 (Claim 1).
In FIG. 9, even if there are some differences in shape and arrangement from the components (members, components, etc.) constituting the inkjet printer 100 shown in FIG. 1 as the first embodiment, basically the same function Constituent elements having the same reference numerals are given the same symbols.

  FIG. 9 is a simplified front view showing the main configuration of the ink jet printer according to the second modification. The ink jet printer 100B of the second modification shown in the figure uses a transport device 24 instead of the transport unit 1 as compared with the ink jet printer 100 of FIG. 1, and the common transport path 56 and the refeed path in FIG. 57, the point that the guide member 58 and the paper discharge reversing unit 53 are removed, the point that the paper feeding unit 52A is used instead of the paper feeding unit 52, and the point that the reversing path 25 is used as a reversing path instead of the detour route 6. Is different.

  Compared with the conveyance unit 1 of FIG. 1, the conveyance device 24 uses a conveyance roller 1A configured to rotate clockwise and counterclockwise as indicated by a double arrow instead of the conveyance roller 1, and FIG. The main difference is that instead of the tip roller 4, a tip roller 4 </ b> A configured to be driven to rotate clockwise or counterclockwise is used. The conveying device 24 includes a conveying belt 10 wound and stretched between the conveying roller 1 </ b> A and the tension roller 2.

  In the reversing path 25, a pair of conveying rollers 27 is disposed as a conveying unit that conveys the single-side printed paper 9. The conveyance roller pair 27 is disposed to compensate for a conveyance load due to a long total distance compared to the detour 6 in FIG. On the downstream side of the sheet conveyance direction X2 with respect to the arrangement portion of the conveyance roller pair 27 in the reversing path 25, there are two locations where the movement trajectory of the sheet has an R shape. The radius of curvature of the R portion upstream of the sheet conveying direction X2 in the reversing path 25 is R1, and the radius of curvature of the R portion downstream of the sheet conveying direction X2 is R2. The relationship between R1 and R2 in the inversion path 25 is configured to satisfy R1 <R2. In addition, illustration of the guide member which comprises the inversion path 25 is abbreviate | omitted for the simplification of a figure.

Compared with the paper feeding unit 52 in FIG. 1, the paper feeding unit 52A uses a new registration roller 26 as registration means, and uses a paper feeding conveyance path 55A in place of the paper feeding conveyance path 55 in FIG. The point is mainly different.
A registration roller 26 that temporarily stops the front end of the unprinted sheet 9 to correct the sheet posture such as skew and feeds it in accordance with the image formation timing with the image forming unit 50 is disposed in the sheet feeding conveyance path 55A. Yes. In addition, illustration of the guide member which comprises 55 A of sheet | seat conveyance paths is abbreviate | omitted for the simplification of a figure.

  The operation of the inkjet printer 100B will be described. The operation in the case of automatically performing double-sided printing that performs printing on the first surface (front surface) and the second surface (back surface) of the paper 9 using the inkjet printer 100B will be described. When printing the first surface of the sheet 9, the sheet 9 separated and conveyed in the same manner as the paper feeding operation of the inkjet printer 100 of FIG. Is temporarily abutted against the stopped registration roller 26 to correct the sheet posture such as skew, and then conveyed in the sheet conveying direction X1 indicated by the arrow through the sheet feeding conveyance path 55A in accordance with the image forming timing. Is done.

Next, the sheet is pressed against the conveying belt 10 via the leading end roller 4A and is simultaneously attracted to the conveying belt 10 and further conveyed by the conveying device 24 in the sheet conveying direction X1 indicated by the arrow on the opposite surface 10a of the conveying belt 10 to form an image. Printing is performed by the recording head 3 of the unit 50. Here, since the transport belt 10 is in a state of being charged by the charging roller 7, the sheet 9 is electrostatically attracted to the transport belt 10 and reaches below the recording head 3, and recording is performed based on the image information. The head 3 is driven and printing is performed on the first surface (front surface) to form a predetermined image.
As a recording method of the image forming apparatus, any type of method such as an ink jet method, a wire dot method, a thermal method, a laser beam method, and the like can be adopted (the same applies to the first and second embodiments described above).

  The paper on which the first side has been printed (printed on one side) waits for the ink to dry with the leading end protruding forward from the position of the recording head 3, and then the driving direction of the transport device 24 is switched. Then, the sheet is switched back and conveyed again to the left in FIG. 9 on the opposite surface 10a of the conveying belt 10, and the position of the branching claw 28 is switched to guide and feed the sheet in the direction of the reverse path 25. In the reversing path 25, while the paper travels in the vicinity of the conveyance roller 27, the paper is reversed so that the first-side printed first surface becomes the lower surface (the image surface side is the lower side of the black triangle). The leading edge of the sheet reaches the position of the sheet sensor 29 provided immediately before the junction point with the leading end roller 4A.

When the leading edge of the paper with the first surface and the second surface reversed reaches the paper sensor 29, the paper sensor 29 is turned on, the drive of the transport device 24 is stopped, and the paper is also stopped at that position. Thereafter, the position of the branch claw 28 is switched again, and at the same time, the driving direction of the transport device 24 is switched again.
Next, the conveyance roller 27 is rotationally driven at the timing when the portion of the conveyance belt 10 charged with the charging roller 7 comes immediately before the leading end roller 4A, and the sheet is pressed against the conveyance belt 10 via the leading end roller 4A. At the same time, it is attracted to the opposite surface 10a of the conveyor belt 10 and conveyed rightward in the figure. When the paper adsorbed on the conveyance belt 10 reaches below the recording head 3, the recording head 3 is driven based on the image information at that position, and a predetermined image is formed on the second surface of the paper and printed on both sides. The discharged paper is discharged to a paper discharge tray (not shown).

In this modification, the following specific operations are performed in the reversing path 25. When the single-side printed paper is conveyed downstream in the sheet conveying direction X2 by the rotation driving of the conveying roller 27, as described above, the first side of the single-side printed paper is the lower surface (the image side is a black triangle). The image surface of the paper that has been printed on one side is directed inward in the R1 and R2 portions. For example, in FIG. 9, when the return direction in which the rear end of the sheet is about to return due to a load is indicated by a white arrow, the non-image surface opposite to the image surface is the outer guide member in the R1 portion on the upstream side in the sheet conveyance direction X2. Since the image surface side opposes the guide surface of the inner guide member at the same time, even the upstream R1 portion having a small radius of curvature does not rub the image surface of the one-side printed paper. . The above points are also the same in the detour 6 of the first and second embodiments.
Incidentally, in FIG. 9, the image surface is also outside in the R2 portion, but since the degree of bending / turning is not as great as that in the R1 portion, it is considered that the load on the paper is small and the rubbing force is weak compared to the R1 portion. Therefore, the occurrence of a problem that the image surface is rubbed is smaller than that in the R1 portion.

  In contrast to the second modification described above, in the conventional reversing path of Patent Document 2 and the like, the image surface that has already been printed on one side is directed to the outer guide surface (inner wall) of the guide member that constitutes the reversing path. There is a risk of a problem that the image surface of the sheet rubs against the outer guide surface due to a load when the end is about to come off.

  In all the above embodiments and modifications, the sheet is reversed after the image is formed on the sheet, but the present invention is not limited to this. For example, there is a switchback path that reverses the front and back of the sheet after image formation and passes through the back surface of the transport belt or the transport path, and then switches back and guides the leading edge of the sheet to the nip (registration) on the transport belt. It may be configured. In that case, if the switchback path is provided with an R shape as in the above embodiment or modification, it is needless to say that the same effect can be obtained.

  As described above, the present invention has been described with respect to specific embodiments and modifications. However, the technology disclosed by the present invention is limited to those exemplified in the embodiments and modifications including the above-described embodiments. However, those skilled in the art can configure various embodiments, modifications, and examples in accordance with the necessity and application within the scope of the present invention. If so, it is clear.

The image forming apparatus according to the present invention is not limited to the ink jet type ink jet printer 100 in the above-described embodiment, but may be, for example, a printer, a plotter, a word processor, a facsimile machine, a copying machine, or a multifunction machine having two or more functions. The present invention can also be applied to an image forming apparatus including an ink jet recording apparatus. Further, the image forming apparatus according to the present invention is not limited to the serial type ink jet printer 100 in the above-described embodiment, but may be applied mutatis mutandis to an image forming apparatus using, for example, a line type ink jet recording apparatus and a conveyance belt that sucks and conveys a sheet. Is possible.
Further, the sheet is not limited to the sheet 9, and includes all sheets that can form an image by an ink jet method, such as usable thin paper, thick paper, postcard, envelope, or OHP sheet as described above.

1,1A Conveyance roller (driving / rotating member)
2 Tension roller (driven / rotating member)
3 Recording head (image forming means)
4 Tip roller (conveyance means, conveyance auxiliary means)
5 Double-sided pressure roller (conveyance means, conveyance auxiliary means)
6,6A Detour (detour route)
7 Charging roller (charging means)
8 Paper tray 9 Paper (sheet, recording medium)
10 Conveying belt (conveying means)
10a Conveying belt facing surface 10b Conveying belt non-facing surface 11 Paper discharge roller (refeeding means, discharging means)
12 spur roller (refeeding means, discharging means)
16 Branching claw (branching means, refeeding means)
19 Paper cassette (sheet storage means)
21 Insertion / Removal Area 24 Transport Device 25 Inversion Path (Inversion Path)
27 Pair of transport rollers (transport means)
50 Image forming unit 51 Conveying unit 52 Paper feeding unit 53 Paper discharge reversing unit 55 Paper feeding conveyance route 56 Common conveyance route 57 Refeeding route (refeeding route, refeeding means)
100, 100A, 100B Inkjet printer (image forming apparatus)
Xa Sub-scanning direction (sheet conveyance direction)
Xb Sheet discharge direction X1, X2 Sheet conveyance direction

JP-A-2006-232440 (Claims, paragraphs “0008”, “0010”, “0012”, FIG. 1, etc.) JP 2005-148365 A

Claims (5)

A conveying belt that is wrapped around at least two rotating members and is circulated and conveys a sheet;
An image forming unit disposed opposite to the conveying belt and forming an image on a sheet conveyed by the conveying belt;
A sheet re-feeding unit that switches back the sheet on which the image has been formed on one side that has passed through the conveying belt, and re-feeds the sheet again to the image forming unit;
A reversing path for reversing the front and back of the sheet on which the single-sided image has been fed that has been fed by the refeeding unit, and again guiding the sheet to the conveying belt surface facing the image forming unit;
In an image forming apparatus having
The reversing path includes at least two places where the movement locus of the sheet guided by the reversing path has a curved R shape,
The R shape on the most downstream side in the sheet conveyance direction in the reversing path is configured to be larger than other R shapes on the upstream side in the sheet conveyance direction, and the R shape portion on the most upstream side in the sheet conveyance direction is configured. The image forming apparatus, wherein the guide surface is configured to bend the image forming surface side of a sheet on which a single-sided image has been formed inward along the sheet conveying direction . The refeeding unit is configured to refeed and guide a sheet on which a single-sided image has been formed to the conveying belt surface on the opposite side that does not face the image forming unit,
The reversing path is configured such that the sheet on which a single-sided image has been formed passes through the conveying belt surface on the opposite side, and then the rotating member on the upstream side of the portion facing the image forming unit in the moving direction of the conveying belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is a detour path that detours around an outer periphery of the wound conveyance belt and guides the surface to the opposite conveyance belt surface.   The image forming apparatus according to claim 1, wherein a distance of the reversing path is set to be equal to or less than a sheet length in the sheet conveying direction in a minimum sheet size that can be used in the image forming apparatus.   The image forming apparatus according to claim 1, wherein the reversing path does not include a conveying unit. It is detachable with respect to the image forming apparatus main body, has a sheet storage means for storing a sheet,
The image forming apparatus according to claim 1, wherein the reversing path is disposed at a position retracted from an insertion / removal region of the sheet storage unit.

Images