JP2005104706A - Sheet conveying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize a sheet conveying device capable of inverting a recording medium without imparting influence such as a roll mark to the recording medium while preventing generation of skew at conveying of the recording medium, and an image forming device. <P>SOLUTION: Load of 20 gf (196.133 mN) is applied to a discharge roll 34 respectively. Nip pressure is applied to a nip part 35 of the discharge roll 34 by the load. An inversion roll 106 is arranged above the discharge roll 34 so as to project to a front surface side. Namely, the inversion roll 106 is arranged at a position more separated from a fixing device 90 than the discharge roll 34. For example, load of 100 gf (980.665 mN) is applied to the inversion roll 106 respectively and normal rotation and reverse rotation are carried out by an inversion motor 108. Nip pressure is applied to a nip part 107 of the inversion roll 106 by the load applied to the inversion roll 106. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet and an image forming apparatus that forms an image on the sheet.

An image forming apparatus generally includes an image forming unit and a sheet conveying unit that conveys a sheet to the image forming unit, and the image forming unit and the sheet conveying unit are accommodated in the main body of the image forming apparatus. In such an image forming apparatus, in order to form an image on both sides of the sheet, the sheet with the image formed on the front surface is reversed, and the sheet is conveyed again to the image forming unit to form an image on the back surface.
Conventionally, as this type of image forming apparatus, it is known to perform double-sided printing by inverting a sheet by attaching a sheet reversing apparatus having a reversing roll to an image forming apparatus main body having a discharge roll (Patent Document). 1).

Japanese Patent Laid-Open No. 10-129912

  However, when the nip pressure of the discharge roll is increased, a roll mark is generated when the toner is not sufficiently solidified on the recording medium on which the image is fixed by the fixing device. On the other hand, if the distance from the fixing device to the discharge roll and the reverse roll is increased in order not to affect the recording medium such as roll marks, the toner is cooled to the extent that the toner is sufficiently solidified. There has been a problem that the sheet conveying device and the image forming apparatus are increased in size.

  SUMMARY OF THE INVENTION An object of the present invention is to downsize a sheet conveying apparatus and an image forming apparatus without affecting the recording medium with a roll mark.

  In order to achieve the above object, the first feature of the present invention is that it has a discharge roll for discharging the recording medium and a reverse roll for reversing the recording medium, and the nip pressure of the reverse roll is the discharge roll. The sheet conveying device is higher than the nip pressure. Therefore, even if the distance from the fixing device or the like to the discharge roll and the reverse roll is not increased, the discharge roll has a low nip pressure, so that it is possible to prevent the recording medium from being affected by a roll mark and the like. Since the roll has a high nip pressure, it is possible to prevent a skew from being generated during conveyance such as a reversing operation of the recording medium, so that the sheet conveying apparatus can be reduced in size.

  Further, the nip pressure of the reverse roll is preferably in the range of 3 to 8 times the nip pressure of the discharge roll. Furthermore, it is preferable that the reversing roll is provided as an option attached to another apparatus.

  The second feature of the present invention is that the image forming unit, a discharge roll that discharges the recording medium on which the image is formed by the image forming unit, and a recording medium that returns the recording medium to the upstream side of the image forming unit. And a reversing roll for reversing the medium, and the nip pressure of the reversing roll is higher than the nip pressure of the discharge roll. The image forming unit includes a fixing member that fixes the toner transferred to the recording medium to the recording medium with heat and pressure, and a distance from the nip portion of the fixing member to the nip portion of the reversing roll is It is preferable that the distance is longer than the distance to the nip portion of the discharge roll. Therefore, even if the distance from the fixing device or the like to the discharge roll is shortened, the discharge roll has a low nip pressure, so that it is possible to prevent the recording medium from being affected by a roll mark. Since the pressure is high, it is possible to prevent a skew from being generated during conveyance such as a reversing operation of the recording medium, so that the image forming apparatus can be downsized.

The toner may have a low melting point. Even when the distance from the fixing device to the discharge roll is short, since the nip pressure of the discharge roll is low, it is possible to prevent the recording medium from being affected by the roll mark, and the reverse roll has a high nip pressure. This is because it is possible to prevent a skew from occurring during conveyance such as a reversing operation of the recording medium.
The toner may be a multi-color toner. When color toner is used compared to black toner, the amount of toner on the recording medium is likely to increase, and images other than characters are likely to increase. It is the best form to do.

  According to the present invention, the sheet conveying apparatus and the image forming apparatus can be reduced in size without affecting the recording medium by a roll mark.

Next, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an outline of an image forming apparatus 10 according to the first embodiment of the present invention. The image forming apparatus 10 according to the first embodiment includes an image forming apparatus main body 12, a detachable cover 13 is provided on the upper portion of the image forming apparatus main body 12, and the back side of the image forming apparatus main body 12. A passage port 14 through which a sheet (recording medium) passes is provided at the bottom (right side in FIG. 1). An opening / closing cover 16 that is rotatable about a rotation fulcrum 15 is provided at the upper part of the image forming apparatus main body 12, and a single-stage sheet supply unit 18 is disposed at the lower part of the image forming apparatus main body 12. Has been.

  The sheet supply unit 18 includes a sheet supply unit main body 20 and a sheet supply cassette 22 in which sheets are stored. A feed roll 24 that supplies sheets from the sheet supply cassette 22 and a retard roll 26 that spreads the supplied sheets one by one are disposed in the upper part near the rear end of the sheet supply cassette 22.

  The conveyance path 28 is a sheet path from the feed roll 24 to the discharge port 30, and this conveyance path 28 is in the vicinity of the back side (right side surface in FIG. 1) of the image forming apparatus main body 12 and is described later from the sheet supply unit 18. The fixing device 90 is formed substantially vertically. A secondary transfer roll 80 and a secondary transfer backup roll 72, which will be described later, are disposed on the upstream side of the fixing device 90 in the conveyance path 28, and the registration roll 32 is located upstream of the secondary transfer roll 80 and the secondary transfer backup roll 72. Is arranged. In addition, a discharge roll 34 is disposed in the vicinity of the discharge port 30 of the conveyance path 28. The discharge roll 34 has a roll width of 10 mm, for example, and is provided in parallel, for example. Further, for example, a load of 20 gf (196.133 mN) is applied to each discharge roll 34. Due to this load, a nip pressure is applied to the nip portion 35 of the discharge roll 34.

  Therefore, the sheet fed from the sheet supply cassette 22 of the sheet supply unit 18 by the feed roll 24 is turned by the retard roll 26 and only the uppermost sheet is guided to the conveyance path 28 and temporarily stopped by the registration roll 32. The toner image is transferred between a secondary transfer roll 80 and a secondary transfer backup roll 72, which will be described later, and the transferred toner image is fixed by the fixing device 90, and the discharge port 34 discharges the discharge port 30. Are discharged to a discharge portion 36 provided on the upper portion of the opening / closing cover 16. The discharge portion 36 has a low discharge port portion and is inclined so as to gradually increase toward the front direction (left direction in FIG. 1).

  In the image forming apparatus main body 12, for example, a rotary developing unit 38 is disposed at a substantially central portion. The rotary developing unit 38 includes developing units 42a to 42d that form toner images of four colors of yellow, yellow, magenta, cyan, and black in the developing unit main body 40, respectively. It rotates counterclockwise (counterclockwise in FIG. 1) about the rotary developer center 44. Each of the developing units 42a to 42d has developing rolls 46a to 46d, and is pressed in the normal direction of the developing unit main body 40 by elastic bodies 48a to 48d such as coil springs.

  The rotary developing unit 38 is arranged so that an image carrier 50 made of, for example, a photosensitive member is in contact therewith, and the developing rolls 46a to 46d are not in contact with the image carrier 50 and have a single outer periphery. The portion protrudes from the outer periphery of the developing device main body 40 in the radial direction, for example, 2 mm. Further, a tracking roll (not shown) having a diameter slightly larger than the diameter of the developing rolls 46a to 46d is provided at both ends of each of the developing rolls 46a to 46d so as to rotate coaxially with the developing rolls 46a to 46d. Yes. That is, the developing rolls 46a to 46d of the developing units 42a to 42d are arranged on the outer periphery of the developing unit main body 40 at intervals of 90 ° around the rotary developing unit center 44, and the tracking rolls of the developing rolls 46a to 46d are imaged. A latent image on the image carrier 50 is abutted against flanges (not shown) provided at both ends of the carrier 50, and a predetermined gap is formed between the developing rollers 46a to 46d and the image carrier 50. Develop with each color toner.

Below the image carrier 50, a charging device 52 made of, for example, a charging roll for uniformly charging the image carrier 50 is provided. An image carrier cleaner 54 is in contact with the image carrier 50 on the upstream side of the charging device 52 in the rotation direction of the image carrier 50. The image carrier cleaner 54 includes, for example, a cleaning blade 56 that scrapes off toner remaining on the image carrier 50 after primary transfer, and a toner collection bottle 58 that collects toner scraped off by the cleaning blade 56.
Note that the back side (the right side in FIG. 1) of the toner collection bottle 58 is formed with, for example, a rib or the like, and is curved so that the sheet is smoothly conveyed to constitute the conveying path 28.

  Below the rotary developing unit 38, an exposure device 60 for writing a latent image on the image carrier 50 charged by the charging device 52 by a light beam such as a laser beam is disposed. Further, an intermediate transfer device 62 is provided above the rotary developing unit 38 to primarily transfer the toner image visualized by the rotary developing unit 38 at the primary transfer position and transport the toner image to a secondary transfer position described later.

The intermediate transfer device 62 includes, for example, an intermediate transfer member 64 such as an intermediate transfer belt, a primary transfer roll 66, a wrap-in roll 68, a wrap-out roll 70, a secondary transfer backup roll 72, a scraper backup roll 74, and a brush backup roll 76. Is done. The intermediate transfer body 64 has elasticity, for example, and is stretched substantially flat so as to have a long side and a short side above the rotary developing unit 38. The intermediate transfer member 64 includes a wrap-in roll 68 disposed upstream of the primary transfer roll 66 below the long side of the intermediate transfer member 64, and a wrap-out roll 70 disposed downstream of the primary transfer roll 66. The image carrier 50 has an image carrier wrap region that comes into contact with the image carrier 50 in a lap shape. The image carrier 50 is wound around the image carrier 50 by a predetermined range and is driven by the rotation of the image carrier 50. As described above, the intermediate transfer member 64 is primarily transferred by the primary transfer roll 66 while superimposing the toner images on the image carrier 50 in the order of, for example, yellow, magenta, cyan, and black, and the primary transferred toner image will be described later. It is conveyed toward the secondary transfer roll 80.
Note that the wrap-in roll 68 and the wrap-out roll 70 are separated from the image carrier 50.

Further, a flat surface portion (short side) is formed on the back side (right side surface in FIG. 1) of the intermediate transfer body 64 by a wrap-out roll 70 and a secondary transfer backup roll 72, and this flat surface portion is subjected to secondary transfer. It faces the conveyance path 28 as a part.
In the secondary transfer portion, the wrap-out roll 70 is arranged so that the intermediate transfer body 64 and the conveyance path 28 are at an angle of 12 °, for example.

  The scraper backup roll 74 assists the scraper 84 described later to scrape off toner remaining on the intermediate transfer body 64 after the secondary transfer, and the brush backup roll 76 removes toner remaining on the intermediate transfer body 64 after the secondary transfer. A brush roll 86 to be described later assists in scraping.

  Above the long side of the intermediate transfer body 64, a sensor 78 such as a reflective photosensor is provided by being fixed to the back surface (inside) of the opening / closing cover 14. The sensor 78 reads a toner patch formed on the intermediate transfer body 64, detects the position of the intermediate transfer body 64 in the rotation direction, and detects the toner density.

  A secondary transfer roll 80 is opposed to the secondary transfer backup roll 72 of the intermediate transfer device 62 with the conveyance path 28 interposed therebetween. That is, the secondary transfer position in the secondary transfer portion is between the secondary transfer roll 80 and the secondary transfer backup roll 72, and the secondary transfer roll 80 is intermediate with the assistance of the secondary transfer backup roll 72. The toner image primarily transferred to the transfer body 64 is secondarily transferred to the sheet at the secondary transfer position. Here, the secondary transfer roll 80 is separated from the intermediate transfer body 64 while the intermediate transfer body 64 rotates three times, that is, while the toner images of three colors of yellow, magenta, and cyan are transported. When the image is transferred, it comes into contact with the intermediate transfer member 64. In addition, a predetermined potential difference is generated between the secondary transfer roll 80 and the secondary transfer backup roll 72. For example, when the secondary transfer roll 80 is set to a high voltage, the secondary transfer backup 80 The roll 72 is connected to a ground (GND) or the like.

  An intermediate transfer body cleaner 82 is in contact with the intermediate transfer device 62 on the side opposite to the secondary transfer position. The intermediate transfer body cleaner 82 is, for example, a scraper 84 that scrapes and cleans toner remaining on the intermediate transfer body 64 after secondary transfer, and a brush roll 86 that scrapes off toner remaining after cleaning by the scraper 84, the scraper 84, and the brush roll The toner collecting bottle 88 collects the toner scraped off by the nozzle 86. The scraper 84 is made of, for example, a thin plate made of stainless steel and is applied with a predetermined voltage. The brush roll 86 is made of, for example, an acrylic brush that has been subjected to a conductive treatment. Further, while the intermediate transfer member 64 conveys the toner image, the scraper 84 and the brush roll 86 are separated from the intermediate transfer member 64 and come into contact with the intermediate transfer member 64 at a predetermined timing. Has been.

  A fixing device 90 is disposed above the secondary transfer position. The fixing device 90 includes a heating roll 92 and a pressure roll 94, and fixes the toner image secondarily transferred to the sheet by the secondary transfer roll 80 and the secondary transfer backup roll 72 to the sheet at the nip portion 97, It is conveyed toward the discharge roll 34. The fixing unit 95 is an integrated unit of the fixing device 90 and the discharge roll 34. The fixing unit 95 is configured such that when the cover 13 is removed from the image forming apparatus main body 12, the back side surface (the right side surface in FIG. 1) is exposed.

  The image forming unit 96 is obtained by integrating the intermediate transfer device 62, the image carrier 50, the charging device 52, the image carrier cleaner 54, and the intermediate transfer member cleaner 82. The image forming unit 96 is disposed immediately below the discharge portion 36 of the opening / closing cover 16. For example, the intermediate transfer device 62 is disposed between the rotary developing device 38 and the fixing device 90 to open the opening / closing cover 16. It is attached and detached by.

FIG. 2 shows an image forming apparatus 100 in which a duplex unit 98 is attached to the image forming apparatus 10 according to the first embodiment of the present invention.
The double-sided unit 98 has a double-sided unit main body 102 and a detachable unit cover 104 at the upper part of the double-sided unit main body 102, and the image forming apparatus main body is removed by removing the cover 13 from the image forming apparatus main body 12. 12 is attached to the upper part on the front side.

In the double-sided unit main body 102, for example, four reversing rolls 106 are provided in parallel on the upper front side (left side in FIG. 2), for example. The reverse roll 106 is disposed so as to protrude to the front side above the discharge roll 34. That is, the reverse roll 106 is disposed at a position farther from the fixing device 90 than the discharge roll 34. Further, the reversing roll 106 sandwiches the sheet with a pressure stronger than that of the discharge roll 34, and is rotated forward and reverse by a reversing motor 108 via gears 136a to 136d described later. The reverse conveyance path 110 is a sheet path from the reverse roll 106 to the registration roll 32 through the passage port 14, and the reverse conveyance path 110 includes a portion formed above the fixing unit 95 and the image forming apparatus 10. And a portion formed substantially vertically on the front side outside. In the reverse conveyance path 110, a conveyance path switching plate 112 is provided in the vicinity of the discharge roll 34. When the conveyance path switching plate 112 is switched, the sheet on which the toner image is fixed by the fixing device 90 is guided toward either the discharge roll 34 or the reverse roll 106. On the downstream side of the transport path switching plate 112 of the reverse transport path 110, transport rolls 114 and 116 are disposed. The transport motor 118 drives the transport rolls 114 and 116 separately from the reverse roll 106.
Thus, by attaching the duplex unit 98 to the image forming apparatus 10, a sheet conveyance system capable of performing duplex printing is formed.

Therefore, when performing duplex printing, the sheet guided to the reverse roll 106 side by the conveyance path switching plate 112 is sent to the front side of the image forming apparatus 10 by the reverse roll 106 until the rear end of the sheet is sent from the fixing device 90. When the trailing edge of the sheet is sent out from the fixing device 90, the reverse roll 106 is reversed and guided toward the transport roll 114. The sheet guided to the conveyance roll 114 is returned to the registration roll 32 again via the conveyance roll 116 and the passage port 14. The sheet is temporarily stopped by the registration roll 32, and the toner image is transferred at a timing. The transferred toner image is fixed by the fixing device 90, guided to the conveyance path switching plate 112, and opened and closed by the reverse roll 106. It is discharged to a discharge portion 36 provided at the top of the cover 16.
As described above, the image forming apparatus 10 constitutes an image forming apparatus capable of performing double-sided printing by attaching the optional double-sided unit 98.
When the sheet is discharged to the discharge unit 36, the conveyance path switching plate 112 may be switched to discharge the sheet from either the discharge roll 34 or the reverse roll 106.

Next, the duplex unit 98 will be described in detail.
FIG. 3 is a perspective view showing the outer surface side of the duplex unit 98. The duplex unit 98 has the duplex unit main body 102 as described above, and a detachable unit cover 104 is provided on the duplex unit main body 102. A double-sided unit opening / closing part 120 is provided on the outer surface (FIG. 3) of the double-sided unit main body 102 so that the vertical portion of the reverse conveyance path 110 is opened and closed. 4 is a perspective view showing the inner surface (attachment surface facing the image forming apparatus main body 12) side of the duplex unit 98. FIG. An upper outer guide 130 described later is exposed on the inner surface side of the duplex unit 98.

  5 to 7 show the configuration around the reverse conveyance path 110 of the duplex unit 98. The reverse conveyance path 110 includes an outer surface side guide portion 122 that guides the sheet on the outer surface side of the duplex unit 98, and an inner guide portion 124 that guides the sheet on the inner surface side of the duplex unit 98. The outer surface side guide part 122 is attached to the lower side of the unit cover 104, for example, a rib-shaped outer guide 126 provided in the double-sided unit opening / closing part 120, a rib-like lower outer guide 128 provided in the double-sided unit body 102, and the unit cover 104. For example, the upper outer guide 130 is formed in a rib shape. The inner guide portion 124 includes an inner guide 132 that is substantially opposite to the outer guide 126 and the lower outer guide 128, and that is provided in the duplex unit main body 102, and an upper inner guide 134 that guides the sheet from below in the vicinity of the reversing roll 106. Is done. The conveyance rolls 114 and 116 convey the sheet between the outer guide 126 and the inner guide 132.

  As shown in FIG. 6, for example, four reversing rolls 106 are provided in parallel, and are arranged so as to protrude to the front side above the discharge roll 34. That is, the reverse roll 106 is disposed at a position farther from the fixing device 90 than the discharge roll 34. The reversing roll 106 has a roll width of 12 mm, for example, and is loaded with a load of 100 gf (980.665 mN), for example. The reversing motor 108 arranges gears 136 a to 136 a located above the duplex unit main body 102. Forward rotation and reverse rotation are performed via 136d. A nip pressure is applied to the nip portion 107 of the reverse roll 106 by the load applied to the reverse roll 106.

As shown in FIG. 4, in the duplex unit 98, the lower surface of the upper outer guide 130 is exposed toward the reverse conveyance path 110. That is, the space between the inner guide 132 and the upper inner guide 134 is opened at the upper lower surface of the duplex unit 98.
FIG. 8 is a perspective view showing the outer shape of the fixing unit 95. The fixing unit 95 includes a fixing device storage unit 138 that stores the heating roll 92 and the pressure roll 94, and a discharge roll storage unit 140 that stores the discharge roll 34. Further, on the upper surface of the fixing unit 95, for example, a rib-shaped outer surface guide 142 is provided, and the conveyance path switching plate 112 of the duplex unit 98 is provided between the fixing device housing portion 138 and the discharge roll housing portion 140. A switching plate hole 144 to be inserted is provided.

  When the duplex unit 98 is attached to the fixing unit 95 at the upper part of the image forming apparatus main body 12, the outer surface guide 142 of the fixing unit 95 is arranged in an open part between the inner guide 132 and the upper inner guide 134. . That is, the cover 13 is removed from the image forming apparatus main body 12 and the duplex unit 98 is attached to the upper part of the image forming apparatus main body 12, whereby the outer surface of the fixing unit 95 is interposed between the inner guide 132 and the upper inner guide 134. A guide 142 is arranged to constitute a reverse conveyance path 110 (see FIGS. 2, 6, and 7).

Next, the roll trace and skew evaluation results for the discharge roll 34 and the reverse roll 106 will be described.
As described above, the discharge roll 34 is housed in the fixing unit 95 together with the fixing device 90, and a load of 20 gf (196.133 mN) is applied. As described above, the reverse roll 106 is disposed at a position farther from the fixing device 90 than the discharge roll 34, and a load of 100 gf (980.665 mN) is applied.
If a large load is applied to the sheet by the discharge roll 34, the sheet will have a roll mark. For example, when carnauba wax having a melting point of 83 ° C. (acid value 8 mg / g, molecular weight 520) is used as the toner release material, the discharge roll 34 is loaded with a load of 30 gf (294.1995 mN) or more to discharge the sheet. When ejected from No. 34, the result was an unacceptable roll mark on the sheet. On the other hand, even when a load of 20 gf (196.133 mN) was applied to the discharge roll 34 and the sheet was discharged from the discharge roll 34, a result was obtained in which almost no roll marks were formed. If the load applied to the discharge roll 34 is in the range of 20 gf (196.133 mN) ± 20%, it can be allowed for the roll marks.
Further, when the load applied to the reversing roll 106 is low, skew occurs at the timing when the reversing roll 106 reverses the sheet. The skew of the timing at which the reverse roll 106 reverses the sheet is 1.7 mm when the load applied to the reverse roll 106 is 50 gf (490.3325 mN), and 0.4 mm when the load is 75 gf (735.49875 mN). In the case of 100 gf (980.665 mN), a result of 0 mm was obtained.
As described above, the reversing roll 106 sandwiches the sheet with a nip pressure stronger than that of the discharge roll 34 to prevent skew when the sheet is reversed, and is disposed at a position farther from the fixing device 90 than the discharge roll 34. This prevents the reversing roll 106 from being left on the sheet.

Next, the operation of the image forming apparatus 10 to which the duplex unit 98 is attached will be described.
When the image forming signal is sent, the image carrier 50 is uniformly charged by the charging device 52, and a light beam is emitted from the exposure device 60 to the charged image carrier 50 based on the image signal. Light rays from the exposure device 60 expose the surface of the image carrier 50 to form a latent image. The latent image on the image carrier 50 formed by the exposure device 60 is developed with yellow, magenta, cyan, and black toner images by the rotary developing unit 38 and is primarily transferred onto the intermediate transfer member 64. In the primary transfer, waste toner remaining on the image carrier 50 is scraped off and collected by the image carrier cleaner 54.

  On the other hand, the sheet stored in the sheet supply cassette 22 is sent out by the feed roll 24 by the sheet supply signal or the like, is turned by the retard roll 26 and guided to the conveyance path 28, is temporarily stopped by the registration roll 32, and the timing is reached. As a result, it is guided between the secondary transfer roll 80 and the secondary transfer backup roll 72. When the sheet is guided between the secondary transfer roll 80 and the secondary transfer backup roll 72, the toner image primarily transferred to the intermediate transfer body 64 is transferred to the sheet by the secondary transfer roll 80 and the secondary transfer backup roll 72. Secondary transfer. Waste toner remaining on the intermediate transfer member 64 after the secondary transfer is scraped off and collected by the intermediate transfer member cleaner 82.

  The sheet to which the toner image has been transferred is guided to the fixing device 90, and the toner image is fixed by the thermal pressure by the heating roll 92 and the pressure roll 94. The sheet on which the toner image is fixed is guided to the conveyance path switching plate 112 and guided to the reverse roll 106. The sheet guided to the reversing roll 106 is fed to the front side of the image forming apparatus 10 by the reversing roll 106 until the rear end of the sheet is fed from the fixing device 90, and is reversed when the rear end of the sheet is fed from the fixing device 90. The roll 106 is reversed and guided to the reverse conveyance path 110 and guided toward the conveyance roll 114. The conveyance rolls 114 and 116 convey the sheet downward and guide it to the registration roll 32 again. The sheet guided to the registration roll 32 is transferred with the toner image again, guided to the conveyance path switching plate 112 through the fixing device 90, and discharged to the discharge unit 36 by the reverse roll 106.

  When the duplex unit 98 is not attached, the image forming apparatus 10 discharges the sheet on which the toner image is fixed from the discharge port 30 to the discharge unit 36 by the discharge roll 34.

1 is a side view showing an image forming apparatus according to a first embodiment of the present invention. 1 is a side view illustrating an image forming apparatus in which a duplex unit is attached to an image forming apparatus according to a first embodiment of the present invention. 1 is a perspective view showing an outer surface side of a duplex unit attached to an image forming apparatus according to a first embodiment of the present invention. 1 is a perspective view showing an inner surface side of a duplex unit attached to an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a perspective view showing a state in which a duplex unit opening / closing part of the duplex unit attached to the image forming apparatus according to the first embodiment of the present invention is opened. FIG. 2 is a perspective view illustrating a state in which a unit cover and a duplex unit opening / closing unit of the duplex unit attached to the image forming apparatus according to the first embodiment of the present invention are opened. 1 is a side view showing a duplex unit attached to an image forming apparatus according to a first embodiment of the present invention. 1 is a perspective view illustrating a fixing unit of an image forming apparatus according to a first embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image forming apparatus main body 13 Cover 14 Passing port 15 Rotation fulcrum 16 Opening / closing cover 18 Sheet supply unit 28 Conveyance path 35,97,107 Nip part 38 Rotary developing device 50 Image carrier 52 Charging device 62 Intermediate transfer device 64 Intermediate transfer body 80 Secondary transfer roll 90 Fixing device 95 Fixing unit 96 Image forming unit 98 Duplex unit 100 Image forming apparatus 102 Duplex unit body 104 Unit cover 106 Reverse roll 110 Reverse transport path 112 Transport path switching plates 114 and 116 Transport roll 122 outer surface side guide portion 124 inner side guide portion 126 outer side guide 130 upper outer surface guide 132 inner side guide 134 upper inner surface guide 142 outer surface guide 144 hole for switching plate

Claims (7)

  A sheet conveying apparatus comprising: a discharge roll for discharging a recording medium; and a reverse roll for reversing the recording medium, wherein the nip pressure of the reverse roll is higher than the nip pressure of the discharge roll.   The sheet conveying apparatus according to claim 1, wherein a nip pressure of the reverse roll is in a range of 3 to 8 times a nip pressure of the discharge roll.   The sheet conveying apparatus according to claim 1, wherein the reversing roll is provided on an option side attached to another apparatus.   An image forming unit, a discharge roll that discharges the recording medium on which an image is formed by the image forming unit, and a reversing roll that reverses the recording medium to return the recording medium to the upstream side of the image forming unit. An image forming apparatus, wherein a nip pressure of a reverse roll is higher than a nip pressure of the discharge roll.   The image forming unit includes a fixing member that fixes the toner transferred to the recording medium to the recording medium with heat and pressure, and the distance from the nip portion of the fixing member to the nip portion of the reversing roll is the discharge roll. The image forming apparatus according to claim 4, wherein the distance is longer than a distance to the nip portion.   6. The image forming apparatus according to claim 5, wherein the toner has a low melting point.   6. The image forming apparatus according to claim 5, wherein the toner is a color toner of a plurality of colors.

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