JP2010215376A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow double-side printing irrespective of the size or type of a paper sheet and downsizing in an image forming device including a paper feed mechanism for feeding the paper sheet, a transfer mechanism for transferring the paper sheet to a printing section, and a double-side unit for printing on a reverse surface of the paper sheet. <P>SOLUTION: The image forming device including an image forming device body that includes an image forming section and a double-side unit 61 that allows printing on a reverse surface by reversing a recording medium having one surface on which an image is formed by the image forming device and feeding the recording medium to the image forming section includes a stretch section A that extends and contracts the length of a double-side transfer path in the double-side unit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement of an image forming apparatus having a double-sided printing function, and more particularly to an image forming apparatus that is capable of performing double-sided printing without being limited by the size and type of paper while being small.

In recent years, many image forming apparatuses such as copiers and printers are provided with a double-sided printing function for forming an image on the back side of a sheet in order to save resources.
In the double-sided printing step, the paper fed from the paper feeding unit is conveyed to the printing unit, printed on the front side, then reversed in the machine, conveyed to the printing unit again, and printed on the back side.
By the way, recently, there is a great demand for a double-sided printing function even in a relatively low speed and small model. On the other hand, when a double-sided unit having a double-sided printing mechanism (paper reversing mechanism) is installed in the image forming apparatus, there is a disadvantage that the size is increased. For this reason, the current duplex unit can be reduced in size by shortening the conveyance path for paper reversal or by reducing its curvature.
However, double-sided units with a shortened transport path and reduced curvature in this way cannot support double-sided printing on paper longer than the transport path length in the double-sided unit, and can also be used for thick paper such as glossy paper, cardboard, and envelopes. On the other hand, since the folding at the time of reversal is not allowed, the double-sided printing is not possible, and there is a problem that the paper size and type capable of double-sided printing are limited.

Japanese Patent Application Laid-Open No. 2001-063019 switches a sheet on which an image is formed on one side in the image forming apparatus main body for the purpose of providing an ink jet recording apparatus capable of duplex printing capable of achieving stable image quality and miniaturization. A configuration is disclosed that includes a reversing unit for back (reversing) and a double-sided conveying path for refeeding a sheet reversed by the reversing unit.
According to this conventional example, the sheet can be reversed, the sheet can be conveyed again to the printing unit, and printing can be performed on the back side. However, when the size is further reduced, there is a limit to the sheet size that can be printed on both sides. Has the problem.
Japanese Patent Application Laid-Open No. 10-338404 discloses the length of the switchback conveyance path after the conveyance path switching means for the purpose of enabling space-saving installation while allowing the sheet long in the conveyance direction to be switched back and conveyed in reverse. Is set to be short so that the entire double-sided reversing device is reduced in size, and a paper path switching member is provided in a direction that does not come into contact with other peripheral devices.
Although this conventional example supports double-sided printing on paper that is long in the transport direction, there is a problem in that there is a limit to the paper size that can be printed on both sides when the size is further reduced.

The present invention has been made in view of the above, and in an image forming apparatus having a paper feed mechanism that feeds paper, a transport mechanism that transports the paper to a printing unit, and a duplex unit that prints the back side of the paper, It is intended to enable double-sided printing without being limited by size and type, and to cope with downsizing.
In particular, since the conveyance path in the duplex unit can be expanded and contracted, the duplex unit can reverse the sheet even for a sheet long in the conveyance direction or a sheet having a large sheet thickness, and duplex printing is possible. .

In order to achieve the above object, the invention according to claim 1 is directed to an image forming apparatus main body provided with an image forming unit, and a recording medium that has undergone image formation on one side by the image forming apparatus, and is sent to the image forming unit. An image forming apparatus having a duplex unit capable of printing on the other side of the image forming apparatus, further comprising: an expansion / contraction portion that allows expansion / contraction change of the length of the duplex conveyance path in the duplex unit. .
According to a second aspect of the present invention, the double-sided conveyance path length is provided by providing an expansion / contraction portion in which a part of the double-sided conveyance path is divided into two members along the recording medium conveyance direction, and adjusting the expansion / contraction of each member. It is characterized in that can be changed.
According to a third aspect of the present invention, the duplex unit has a plurality of pairs of reversing rollers for reversing the paper and rollers in contact with the reversing rollers, and the expansion / contraction section has two parts that avoid the reversing rollers. A separate structure is provided, and comb teeth that mesh with each other are provided at the end of each member.
According to a fourth aspect of the present invention, the duplex unit includes a plurality of pairs of reversing rollers for reversing paper and rollers in contact with the reversing rollers, and the extendable portion has two parts that avoid the reversing rollers. It is characterized by having a divided structure and a structure in which individual members are connected in a foldable manner.

According to a fifth aspect of the present invention, the duplex unit includes a fixed unit lower part and a movable unit upper part, and the unit upper part is lifted with respect to the unit lower part, whereby the interval between the comb teeth, or The distance between the two members is changed, and the double-sided conveyance path length is extended.
6. The image forming apparatus according to claim 5, wherein the reversing roller maintains a nip state with the roller of the double-sided unit even when the upper part of the double-sided unit is lifted. It is a device.
The invention of claim 7 is characterized in that in the double-sided unit, the interval between the comb teeth can be changed in one stage or in multiple stages.
According to an eighth aspect of the present invention, when the upper portion of the double-side unit is lifted, the comb tooth portion is located on the inner side of the conveyance path with the comb tooth tip portion positioned on the upper side than the comb tooth tip portion positioned on the lower side. It is characterized by doing.
The invention of claim 9 is characterized in that, in a state where the folding portion is folded, the member on the downstream side in the transport direction is located outside the member on the upstream side.
According to a tenth aspect of the present invention, the duplex unit is detachable from the main body of the image forming apparatus.

According to the present invention, in an image forming apparatus having a paper feed mechanism that feeds paper, a transport mechanism that transports the paper to the printing unit, and a duplex unit that prints the back surface, the paper size and type are limited. Therefore, both sides can be printed, and miniaturization can be supported.
In particular, since the conveyance path in the duplex unit can be expanded and contracted, the duplex unit can reverse the sheet even for a sheet long in the conveyance direction or a sheet having a large sheet thickness, and duplex printing is possible. .

1 is an explanatory diagram of an internal configuration of an image forming apparatus according to an embodiment of the present invention, more specifically a cross-sectional view of an ink jet recording apparatus. It is a top view which shows the structure of the image recording part vicinity in FIG. FIG. 2 is a cross-sectional view of a part of the exterior of the inkjet recording apparatus duplex unit in FIG. It is sectional drawing of the double-sided unit comb-tooth part in FIG. It is sectional drawing of the double-sided unit comb-tooth part in 3rd Embodiment. It is a structure and operation | movement explanatory drawing of the double-sided unit which concerns on the 4th Embodiment of this invention.

Hereinafter, an ink jet recording apparatus as an example of an image forming apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is an explanatory diagram of an internal configuration of an image forming apparatus according to an embodiment of the present invention, more specifically a cross-sectional view of an ink jet recording apparatus, and FIG. 2 is a configuration in the vicinity of an image recording unit in FIG. FIG.
The ink jet recording apparatus is roughly configured from an image forming main body having an image forming unit and a double-sided unit attached to the image forming apparatus main body.
The ink jet recording apparatus holds a carriage 3 slidably in a main scanning direction by a guide rod 1 which is a guide member horizontally mounted on left and right side plates (not shown), and is driven between a driving pulley 6a and a driven pulley 6b by a main scanning motor 4. The moving scanning is performed in the main scanning direction indicated by the arrow in FIG. Note that guide bushes (bearings) 3a and 3a are interposed between the carriage 3 and the guide rod 1, respectively.

The carriage 3 includes, for example, four recording heads 7 each including a droplet discharge head that discharges yellow (Y), cyan (C), magenta (M), and black (Bk) ink droplets. The outlets are arranged in a direction crossing the main scanning direction, and the ink droplet ejection direction is directed downward.
As a droplet discharge head constituting the recording head 7, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses film boiling of a liquid using an electrothermal transducer such as a heating resistor, or a metal phase change due to a temperature change is used. For example, a shape memory alloy actuator, an electrostatic actuator using an electrostatic force, or the like provided as energy generating means for discharging ink (recording liquid) can be used.
On the carriage 3, sub tanks for each color (not shown) for supplying ink of each color to the recording head 7 are mounted. Ink is supplied to the sub tank from a main tank (ink cartridge) (not shown) via an ink supply tube. In addition to the recording head 7 that discharges ink droplets, a recording head that discharges a fixing treatment liquid (fixing ink) that reacts with the recording liquid (ink) to improve the fixing property of the ink can be provided.

On the other hand, as a paper feeding unit for feeding paper 12 stacked on a paper stacking unit (pressure plate) 11 such as a paper feeding cassette 10, a paper feeding roller for separating and feeding the paper 12 from the paper stacking unit 11 one by one. 13 is provided with a separation pad 14 made of a material having a large friction coefficient, and this separation pad 14 is urged toward the paper feed roller 13 side.
As a transport unit for transporting the recording medium (paper) 12 fed from the paper feed unit below the recording head 7, a transport belt 21 for attracting and transporting the paper 12 with electrostatic force; A counter roller 22 for transporting the paper 12 fed from the paper supply unit via the guide 15 between the transport belt 21 and the paper 12 fed substantially vertically upward, the direction of the paper 12 being changed by approximately 90 °, and the transport belt. 21 is provided with a conveyance guide 23 for following the upper surface 21 and a tip pressure roller 25 urged toward the conveyance belt 21 by a pressing member 24. In addition, a charging roller 26 constituting a charging unit for charging the surface of the transport belt 21 is provided.
Here, the conveyance belt 21 is an endless belt, is stretched between the conveyance roller 27 and the tension roller 28, and the conveyance roller 27 rotates from the sub-scanning motor 31 via the timing belt 32 and the timing roller 33. By doing so, it is configured to circulate in the belt conveyance direction (sub-scanning direction) of FIG. A guide member 29 is disposed on the back side of the conveying belt 21 corresponding to the image forming area by the recording head 7.

Further, as shown in FIG. 2, a slit disk 34 is attached to the shaft of the transport roller 27, and a sensor 35 for detecting the slit of the slit disk 34 is provided. An encoder 36 is configured.
The charging roller 26 is disposed so as to come into contact with the surface layer of the conveyor belt 21 and to be rotated by the rotation of the conveyor belt 21, and applies pressure to both ends of the shaft.
As shown in FIG. 1, an encoder scale 42 having slits is provided on the front side of the carriage 3, and an encoder sensor comprising a transmissive photosensor that detects the slits of the encoder scale 42 on the front side of the carriage 3. 43 are provided, and an encoder 44 for detecting the position of the carriage 3 in the main scanning direction is configured by these.
Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 7, a separation claw 51 for separating the paper 12 from the transport belt 21, a paper discharge roller 52 and a paper discharge roller 53, and a discharge And a paper discharge tray 54 for stocking the paper 12 to be printed.

A duplex unit 61 is mounted on the back of the image forming apparatus main body. The duplex unit includes reversing rollers 63a and 63b arranged along a circumferential duplex conveying path, rollers 64a and 64b in contact with the reversing rollers, and a conveying guide unit that forms a circumferential duplex conveying path. 62. Here, the length of the reverse path of the duplex unit 61 is longer than the length of the sheet 12, and when the sensor (not shown) detects that the rear end of the sheet 12 has entered the duplex unit 61, the leading edge of the sheet 12 is detected. Is set to a length that does not reach the conveyor belt 21. With this setting, the entire sheet 12 is taken into the duplex unit 61 without leaving the sheet 12 in the main body of the image forming apparatus.
In addition, the conveyance direction (direction indicated by the arrow in FIG. 1) in the double-sided sheet feeding unit 61 does not change regardless of whether the sheet drive system on the image forming apparatus main body is rotated forward or backward. The drive system for driving the paper conveyance system provided in the double-sided paper feeding unit 61 is composed of, for example, a gear train composed of an odd number of gears on a bracket that swings in accordance with the rotation direction, and an even number of gears. There are two gears connected to the two gear trains, and either one of the gear trains is engaged with the rotation direction of the paper transport system on the apparatus main body side, so that in the double-sided paper feed unit 61 The rotation is kept in one direction. In addition to the swinging bracket, a one-way clutch or an electromagnetic clutch may be used.

In the ink jet recording apparatus configured as described above, the paper 12 is separated and fed one by one from the paper feed unit, and the paper 12 fed substantially vertically upward is guided by the guide 15, and includes the transport belt 21 and the counter roller 22. The leading end is guided by the conveying guide 23 and pressed against the conveying belt 21 by the leading end pressing roller 25, and the conveying direction is changed by approximately 90 °.
At this time, an alternating voltage is applied to the charging roller 26 so that a positive (positive) output and a negative (negative) output are alternately repeated, that is, an alternating voltage is applied to the conveying belt 21 in the sub-scanning direction, which is the circumferential direction. , Plus and minus charges are alternately applied in a strip shape with a predetermined width. When the sheet 12 is fed onto the conveyance belt 21 charged alternately with plus and minus, the sheet 12 is attracted to the conveyance belt 21 by electrostatic force, and the sheet 12 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 21. Is done.

Therefore, by driving the recording head 7 according to the image signal while moving the carriage 3, the ink droplets are ejected onto the stopped paper 12 to record one line, and after the paper 12 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 12 has reached the recording area, the recording operation is finished, and the paper 12 is discharged onto the paper discharge tray 54.
As for the relationship between the scanning direction of the carriage 3 and printing, there are a unidirectional recording mode in which an image is formed only during scanning in one direction and a bidirectional recording mode in which an image is formed in both directions of scanning of the carriage 3. It is optional to set this according to the designation from the user and the print image, or to perform only one of the modes.
In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 12 is fed into the double-side unit 61 by rotating the conveyor belt 21 in the reverse direction. Is reversed (with the back surface being the printing surface), the paper is fed again between the counter roller 22 and the conveyor belt 21, the timing is controlled, and the sheet is conveyed onto the conveyor belt 21 as described above. After recording on the back side, the sheet is discharged onto the discharge tray 54.

Next, a first embodiment of the present invention will be described.
FIG. 3 is a cross-sectional view of a part of the exterior of the double-side unit of the ink jet recording apparatus in FIG. 1 in a comb shape, and FIG. 4 is a cross-sectional view of the double-side unit comb portion in FIG.
As described in the configuration of the ink jet recording apparatus, the length of the reversing path of the duplex unit 61 is made so that the entire sheet 12 is taken into the duplex unit 61 without the sheet 12 remaining in the main body of the inkjet recording apparatus. Is set to a value that is longer than the length of the paper 12 in the transport direction and that the leading edge of the paper 12 does not reach the transport belt 21 when a sensor (not shown) detects that the rear end of the paper 12 has entered the duplex unit 61. There is a need to.
However, if configured in this way, double-sided printing can be performed only on a sheet of a length that can accommodate the entire length in the double-sided conveyance path in the double-sided unit 61. This causes a problem that the number of sheets that can be printed is limited. In order to solve this problem, in the present invention, by extending a part of the double-sided conveyance path in the double-sided unit 61, the double-sided conveyance path length is extended, the curvature of the double-sided conveyance path is increased, and the conveyance direction is increased. In addition, it is possible to reverse in the duplex unit 61 even for a long sheet, a glossy sheet, a thick sheet, or a sheet having a large sheet thickness such as an envelope. Therefore, it is possible to obtain an effect of increasing the types of paper that can be printed on both sides.

As a specific configuration for that purpose, in the duplex unit 61, the reversing roller 63a and the roller 64a, and the reversing roller 63b and the roller 64b are not in contact with each other. The expansion / contraction part A which consists of was provided. The comb teeth 65a and the comb teeth 65b are double-sided by overlapping each other as shown in FIG. 1 when printing on both sides of plain paper (A4 size frequently used in a normal office environment) or paper with a short conveyance direction length. The transport path length is shortened.
In this way, the expansion / contraction part A for expanding / contracting the double-sided conveyance path is formed in a comb-teeth shape that meshes with each other, so that the double-sided conveyance path can be expanded / contracted with a simple configuration and at a low cost. Since powder and mist can be discharged, a stable conveyance effect in the duplex unit 61 can be obtained.
Other operations are the same as those in the basic configuration embodiment of the ink jet recording apparatus, and thus the description thereof is incorporated.

Next, a second embodiment of the present invention will be described with reference to FIG.
The image forming apparatus according to the second embodiment is provided with an expansion / contraction portion A in which a part of a double-sided conveyance path is divided into two members (a double-sided unit upper part 61A and a double-sided unit lower part 61B) along the recording medium conveying direction. A feature is that the double-sided conveyance path length can be changed by adjusting the distance between the members.
That is, in this embodiment, the duplex unit 61 is composed of a movable upper part 61A and a fixed lower part 61B, and the upper part 61A is lifted, and as shown in FIG. The teeth 65a and the comb teeth 65b are separated from each other and fixed at a certain location. There is also a method of pulling down the comb teeth 65a and the comb teeth 65b and pulling down the duplex unit lower portion 61B in order to extend the duplex transport path in the duplex unit 61, but the gap between the duplex unit lower portion 61A is narrow and difficult to operate. In order to improve performance, the upper portion 61A is lifted.
Further, when the comb teeth 65a and the comb teeth 65b are separated (the conveyance path in the double-sided unit 61 is extended), the upper (inner) comb teeth 65a are inward of the double-side conveyance path with respect to the comb teeth 65b. To position.

Furthermore, in the present embodiment, the reverse roller 63a and the roller 64a form a nip even if the duplex conveyance path length in the duplex unit 61 changes.
In the above configuration, the conveyance path length in the duplex unit 61 expands and contracts, so that not only the number of paper types compatible with duplex printing can be increased, but also the size can be reduced. Further, by installing the comb teeth 65a inside the double-sided conveyance path, stable paper conveyance can be obtained.
As a means for lifting the upper part of the double-sided unit 61, a button type using a spring material can be adopted in addition to the method of directly holding the upper part of the double-sided unit manually by the user and lifting it vertically.
Since other operations are the same as the basic configuration of the ink jet recording apparatus, the description thereof is incorporated.

Next, a third embodiment of the present invention will be described. FIG. 5 is a cross-sectional view of a double-sided unit comb tooth portion in the third embodiment.
The comb tooth portion (expandable portion A) of the double-sided unit 61 according to the third embodiment includes spring materials 66a and 66b such as springs or leaf springs between opposing ends of both the comb teeth 65a and the comb teeth 65b. Since it is connected between both comb teeth, it can be expanded and contracted in one stage or in multiple stages.
Since the double-sided conveyance path length and curvature in the duplex unit 61 can be selected according to the paper length and thickness, not only the number of paper types compatible with double-sided printing is increased, but also stable conveyance for each paper is provided. You can also. Moreover, since it is a simple structure, it is inexpensive.
Other operations are the same as those in the basic configuration embodiment of the ink jet recording apparatus, and thus the description thereof is incorporated.

Next, a fourth embodiment of the present invention will be described. FIG. 6 is a cross-sectional view of the duplex unit in the fourth embodiment.
The expansion / contraction part A of the double-sided unit according to the fourth embodiment is characterized in that the folding part 67 is used instead of the comb teeth 65a and 65b of the double-sided unit 61 according to the first embodiment.
The folding portion 67 includes a fixed shaft 90a provided at the end of the unit upper portion 61A, a movable shaft 90b provided at the end of the unit lower portion 61B, and a link 90c that connects the fixed shaft 90a and the movable shaft 90b. The unit lower part 61B is deformed (moved) between the shortened state shown in (a), the intermediate state shown in (b), and the extended state shown in (c) with the fixed shaft 90a as the center. Can do.
That is, the folding unit 67 is located outside the conveyance path of the duplex unit 61 when the conveyance path of the duplex unit 61 is normal (the conveyance path is not extended) (state of FIG. 6A). About the level | step difference between the unit upper part and unit lower part which arises in the folded shortened state, the conveyance part upstream side (reverse roller 63a and roller 64a side) is provided high, and the downstream (reverse roller 63b and roller 64b side) is provided low. Thus, the paper 12 can be transported without being caught by the folding portion step.

As in the case of the second embodiment, by lifting the upper portion 61A of the double-sided unit 61 as shown in FIG. 6B, the folded portion 67 in the folded state is stretched and fixed with the stretched portion fully opened. (FIGS. 6B and 6C). By using the folding part as the expansion / contraction part of the conveyance path, the entire conveyance part of the duplex unit 61 can be covered in a state where the conveyance path is extended, and thus stable conveyance can be provided.
Even if the transport path length in the duplex unit 61 changes, the reversing roller 63a and the roller 64a can form a nip.
Other effects are the same as in the second embodiment.
Other operations are the same as those in the basic configuration embodiment of the ink jet recording apparatus, and thus the description thereof is incorporated.

Next, a fifth embodiment of the present invention will be described.
In the present embodiment, the duplex unit 61 can be detached (detached) from the inkjet recording apparatus main body, and when the duplex unit 61 is detached from the inkjet recording apparatus main body, the vicinity of the transport roller 27 is opened to the outside, The paper jam occurring near the conveyor belt 21 can be processed.
Further, by removing the double-sided unit from the recording apparatus main body when replacing the internal parts of the double-sided unit 61, it is possible to obtain an effect of improving maintainability.
Other operations are the same as those in the basic configuration embodiment of the ink jet recording apparatus, and thus the description thereof is incorporated.
As described above, according to the present invention, in an image forming apparatus having a paper feed mechanism that feeds paper, a transport mechanism that transports paper to a printing unit, and a duplex unit for printing the back side, It is possible to perform double-sided printing without limitation and to cope with downsizing.
In particular, since the conveyance path in the duplex unit can be expanded and contracted, the duplex unit can reverse the sheet even for a sheet long in the conveyance direction or a sheet having a large sheet thickness, and duplex printing is possible. .

  DESCRIPTION OF SYMBOLS 1 ... Guide rod, 3 ... Carriage, 4 ... Main scanning motor, 6a ... Drive pulley, 6b ... Driven pulley, 7 ... Recording head, 10 ... Paper feed cassette, 11 ... Paper stacking part, 12 ... Paper, 13 ... Paper feed Roller, 14 ... Separation pad, 15 ... Guide, 21 ... Conveyor belt, 22 ... Counter roller, 23 ... Conveyor guide, 25 ... End pressure roller, 26 ... Charging roller, 27 ... Conveyor roller, 28 ... Tension roller, 29 ... Guide member, 31 ... sub-scan motor, 32 ... timing belt, 33 ... timing roller, 34 ... slit disk, 35 ... sensor, 36 ... encoder, 42 ... encoder scale, 43 ... encoder sensor, 44 ... encoder, 5 ... timing Belt 51, separation claw 52, discharge roller 53, discharge roller 54, discharge tray 61, duplex unit 61 A Upper part, 61B ... Lower part of unit, 62 ... Conveying guide part, 63a ... Reverse roller, 63b ... Reverse roller, 64a ... Roll, 64b ... Roll, 65a ... Comb teeth, 65a ... Both comb teeth, 65b ... Comb teeth, 90a ... fixed axis, 90b ... movable axis, A ... telescopic part 90c ... link

JP 2001-063019 A JP 10-338404 A

Claims (10)

An image forming apparatus main body having an image forming unit, and a duplex unit capable of printing on the other side by inverting a recording medium that has undergone image formation on one side by the image forming apparatus and sending it to the image forming unit In an image forming apparatus comprising:
An image forming apparatus, comprising: an expansion / contraction section that enables expansion / contraction change of a length of a double-sided conveyance path in the double-side unit.   The double-sided conveyance path length can be changed by providing an expansion / contraction part in which a part of the double-sided conveyance path is divided into two members along the recording medium conveyance direction and adjusting the expansion / contraction of the interval between the individual members. The image forming apparatus according to claim 1, wherein:   The double-sided unit has a plurality of pairs of reversing rollers for reversing paper and rollers in contact with the reversing rollers, and the extendable part has a configuration in which a portion avoiding the reversing rollers is divided into two members, The image forming apparatus according to claim 1, wherein the end portions of the members are provided with comb teeth that mesh with each other.   The double-sided unit has a plurality of pairs of reversing rollers for reversing paper and rollers in contact with the reversing rollers, and the extendable part has a configuration in which a portion avoiding the reversing rollers is divided into two members, The image forming apparatus according to claim 1, further comprising a foldable connection between the members.   The duplex unit includes a fixed unit lower part and a movable unit upper part, and by lifting the unit upper part with respect to the unit lower part, the interval between the comb teeth or the interval between the two members The image forming apparatus according to claim 3, wherein the double-sided conveyance path length is increased.   The image forming apparatus according to claim 5, wherein the reversing roller maintains a nip state with a roller of the duplex unit even when the upper portion of the duplex unit is lifted.   7. The image forming apparatus according to 3, 5, or 6, wherein the double-sided unit can change the interval between the comb teeth in one stage or multiple stages.   The comb-tooth portion is characterized in that when the unit upper portion of the duplex unit is lifted, the comb-tooth tip portion located on the upper side is positioned inside the transport path with respect to the comb-tooth tip portion located on the lower side. Item 8. The image forming apparatus according to Item 3, 5, 6, or 7.   5. The image forming apparatus according to claim 4, wherein the member on the downstream side in the conveyance direction is positioned outside the member on the upstream side in a state in which the folding portion is folded.   The image forming apparatus according to claim 1, wherein the duplex unit is detachable from the main body of the image forming apparatus.

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