JP2017030907A - Sheet conveyance device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveyance device configured to use a crown-shaped separation roller, the device being capable of preventing a sheet separated off a belt from being caught on a guide member, and also to provide an image forming apparatus comprising such a sheet conveyance device.SOLUTION: A guide member 20 is configured to be nearer to a rotation center C of a separation roller 83 which is normal crown-shaped at the ends rather than in a middle portion in a thrust direction of a sheet passage region such that both ends of a sheet P separated off a belt 81 in the rotational axis direction of the separation roller 83 are hung down to prevent the sheet from being caught on the guide member 20.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet by an endless belt stretched between a plurality of stretching rollers, and an image forming apparatus including the sheet conveying apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method or an electrostatic recording method, an electrophotographic photosensitive member (photosensitive member) or an image carrier (first image carrier) which is an electrostatic recording dielectric is appropriately used. A toner image is formed in the image forming process. The toner image is directly transferred to a sheet (transfer material, recording material, recording medium) or temporarily transferred to an intermediate transfer member (second image carrier) and then secondarily transferred to the sheet.

  The electrophotographic image forming apparatus of the intermediate transfer system having the intermediate transfer member will be further described as an example. Such an image forming apparatus is provided with a secondary transfer member that forms a secondary transfer portion in contact with the intermediate transfer member. By applying a voltage to the secondary transfer member, the intermediate transfer member and the secondary transfer member are formed. The toner image is secondarily transferred from the intermediate transfer member onto the sheet that is nipped and conveyed with the transfer member.

  Further, in order to improve the separation performance of the thin paper in the secondary transfer unit, a secondary transfer apparatus provided with an endless belt (hereinafter also simply referred to as “belt”) stretched around a plurality of stretch rollers. A configuration using this is also known (Patent Document 1).

  Further, in such a configuration, in order to improve the separation performance of the sheet from the belt, the separation roller arranged at the separation portion of the sheet from the belt among the plurality of stretching rollers has a regular crown shape. A crown roller has been proposed (Patent Document 2).

  Further, a guide member that guides the sheet separated from the belt further downstream may be provided downstream of the separation roller in the sheet conveyance direction (Patent Document 3). In general, the guide member is disposed substantially parallel to the rotation axis of the separation roller, and the distance between the guide member and the rotation center of the separation roller is substantially the entire region of the guide member in the rotation axis direction of the separation roller. Be made equal.

JP 2012-237911 A Japanese Patent Application No. 2010-86485 JP 2007-79310 A

  However, in a configuration using a separation roller having a regular crown shape, if the distance between the guide member and the rotation axis of the separation roller is substantially equal throughout the guide member, jamming (paper jam) is likely to occur. I understood. In particular, when paper having a relatively small basis weight (so-called thin paper) is used as a sheet, both end portions in the conveying direction hang down and are easily caught by the guide member, and jamming is likely to occur.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a sheet conveying apparatus capable of suppressing a sheet separated from a belt from being caught on a guide member, and an image forming apparatus including the same, in a configuration using a separation roller having a crown shape. Is to provide.

  The above object is achieved by the sheet conveying apparatus and the image forming apparatus according to the present invention. In summary, the present invention relates to a rotatable endless belt that carries and conveys a sheet, and a plurality of stretching rollers that stretch the belt, the tensioning of the sheet being placed from above. A plurality of stretching rollers including an upstream roller disposed upstream in the rotation direction of the belt and a separation roller disposed downstream in the rotation direction of the belt and separating the sheet from the belt. And a guide member disposed in a non-contact manner with respect to the belt for guiding a sheet separated and conveyed from the belt, and the separation roller has an outer diameter at a central portion in a rotation axis direction. In the sheet conveying apparatus, which is a positive crown roller having a positive crown shape larger than the outer diameter of the part, the guide member is a sheet in the rotation axis direction of the separation roller In the cross section substantially perpendicular to the rotation axis of the separation roller, the central guide section in the sheet conveyance direction has a central guide section and an end guide section that respectively guide the sheet at the center and both ends of the passing area. The upstream end is below the belt tangent to the outer circumference of the upstream roller and the outer circumference of the maximum diameter of the separation roller, and is at the same height as the rotation center of the separation roller or higher than the rotation center. The upper end portion of the end guide portion in the sheet conveying direction is located below the tangent line of the belt contacting the outer periphery of the upstream roller and the outer periphery of the minimum diameter of the separation roller, and It is located at the same height as the rotation center of the separation roller or above the rotation center, and the upstream end in the sheet conveyance direction of the central guide portion and the rotation center of the separation roller Than the distance of a sheet conveying apparatus characterized by the smaller of the distance between the center of rotation of the upstream-side end portion and the separation roller in the conveyance direction of the sheet of the end guide portion.

  According to another aspect of the present invention, an image forming apparatus for forming an image on a sheet with toner includes the sheet conveying apparatus of the present invention.

  According to the present invention, in the configuration using the separation roller having a crown shape, it is possible to suppress the sheet separated from the belt from being caught on the guide member.

1 is a schematic cross-sectional view of an image forming apparatus. It is a schematic diagram of the separation roller and the tension roller of the belt unit. FIG. 6 is a schematic diagram for explaining the wrinkling behavior of a sheet in a transfer unit. It is a schematic diagram which shows the arrangement | positioning relationship between a post-separation guide and a separation roller. FIG. 6 is a schematic diagram for explaining the behavior of a sheet after being separated from a secondary transfer belt. It is a typical perspective view for demonstrating the generation | occurrence | production factor of sheet | seat jam. It is a typical top view which shows the arrangement | positioning relationship between the post-separation guide and separation roller in a comparative example. It is a typical side view which shows the arrangement | positioning relationship between the post-separation guide and separation roller in a comparative example. FIG. 3 is a schematic top view showing a positional relationship between a post-separation guide and a separation roller in Embodiment 1. FIG. 3 is a schematic side view illustrating a positional relationship between a post-separation guide and a separation roller in Embodiment 1. FIG. 10 is a schematic top view illustrating a positional relationship between a post-separation guide and a separation roller in Embodiment 2.

  Hereinafter, a sheet conveying apparatus and an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[Example 1]
1. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type laser beam printer that employs an intermediate transfer method that can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes, as a plurality of image forming units (stations), first, second, third, and third images that form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively. A fourth image forming unit SY, SM, SC, SK is included. In this embodiment, the configuration and operation of these four image forming units SY, SM, SC, and SK are substantially the same except that the color of the toner used in the developing process described later is different. Therefore, hereinafter, unless there is a particular need for distinction, Y, M, C, and K at the end of a symbol representing an element for any color will be omitted, and the element will be described generally.

  The image forming unit S includes a photosensitive drum 1 that is a rotatable drum-type electrophotographic photosensitive member (photosensitive member) as a first image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure. In the image forming unit S, the following process devices are arranged around the photosensitive drum 1 in order along the rotation direction. First, a charger 2 as a charging unit is arranged. Next, an exposure device (laser scanner) 3 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 that is a roller-type primary transfer member as a primary transfer means is disposed. Next, a drum cleaner 6 as a photosensitive member cleaning means is disposed.

  The surface of the rotating photosensitive drum 1 is charged almost uniformly by a charger 2 to a predetermined potential having a predetermined polarity (negative polarity in this embodiment). The surface of the charged photosensitive drum 1 is exposed based on the image information by the exposure device 3, and an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) using toner as a developer by the developing device 4, and a toner image is formed on the photosensitive drum 1. In this embodiment, a reversal development method is used. That is, the toner charged with the same polarity as the charged polarity of the photosensitive drum 1 adheres to the exposed portion on the photosensitive drum 1 where the absolute value of the potential is lowered by being exposed after being uniformly charged. In this embodiment, the charging polarity (normal charging polarity) of the toner during development is negative.

  The electrostatic latent image formed by the exposure device 3 is an aggregate of small dot images, and the density of the toner image formed on the photosensitive drum 1 can be changed by changing the density of the dot images. Can do.

  It is composed of a rotatable endless belt as a second image carrier so as to be in contact with the surface of each photosensitive drum 1Y, 1M, 1C, 1K of each image forming unit SY, SM, SC, SK. An intermediate transfer belt 7 that is an intermediate transfer member is disposed. The intermediate transfer belt 7 is stretched around a tension roller 71, a driving roller 72, and a secondary transfer counter roller 73 as a plurality of stretching rollers (support members). The tension roller 71 controls the tension of the intermediate transfer belt 7 to be constant. The driving roller 72 transmits driving force from a driving motor (not shown) as driving means to the intermediate transfer belt 7 to move (rotate) the intermediate transfer belt 7. The intermediate transfer belt 7 is rotationally driven by a driving roller 72 in the direction of arrow R2 in the figure. In this embodiment, the peripheral speed of the intermediate transfer belt 7 is 250 to 300 mm / sec. The secondary transfer counter roller 73 faces a secondary transfer roller 82 (described later) via the intermediate transfer belt 7 and a secondary transfer belt 81 (described later) to form a secondary transfer portion (secondary transfer nip) N2.

  The primary transfer rollers 5Y, 5M, 5C, and 5K described above are disposed on the inner peripheral surface (back surface) side of the intermediate transfer belt 7 in correspondence with the photosensitive drums 1. The primary transfer roller 5 is urged toward the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 7 and the photosensitive drum 1 are in contact with each other. Further, on the outer peripheral surface (front surface) side of the intermediate transfer belt 7, a secondary transfer device 11 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 73. As will be described in detail later, the secondary transfer device 11 includes a secondary transfer belt 81 as a sheet conveying member constituted by an endless belt and a secondary transfer belt 81 disposed on the inner peripheral surface side of the secondary transfer belt 81. And a secondary transfer roller 82 as a transfer member. The secondary transfer roller 82 is urged toward the secondary transfer counter roller 73 via the intermediate transfer belt 7 and the secondary transfer belt 81, so that the intermediate transfer belt 7 and the secondary transfer belt 81 are in contact with each other. Part (secondary transfer nip) N2 is formed. Further, an intermediate transfer belt cleaner 74 serving as an intermediate transfer member cleaning unit is disposed at a position facing the driving roller 72 on the outer peripheral surface side of the intermediate transfer belt 7.

  The toner image formed on the photosensitive drum 1 as described above is electrostatically transferred (primary transfer) onto the rotating intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer portion N1. . At this time, a primary transfer bias (primary transfer voltage) having a polarity (positive in this embodiment) opposite to the normal charging polarity of the toner is applied to the primary transfer roller 5. Thereby, the primary transfer current is supplied to the primary transfer portion N1. For example, when forming a full-color image, the toner images of the respective colors formed on the respective photosensitive drums 1Y, 1M, 1C, and 1K are transferred so as to be sequentially superimposed on the intermediate transfer belt 7 in each primary transfer portion N1. As a result, a multi-toner image for a full color image in which four color toner images are superimposed on the intermediate transfer belt 7 is formed. Deposits such as toner (primary transfer residual toner) remaining on the photosensitive drum 1 after the primary transfer step are removed from the photosensitive drum 1 by the drum cleaner 6 and collected.

  The toner image formed on the intermediate transfer belt 7 is sent to the secondary transfer nip portion N2 by the rotation of the intermediate transfer belt 7. On the other hand, sheets (transfer material, recording material, recording medium) P such as paper (recording paper) stored in a cassette (not shown) are fed one by one by a feeding roller (not shown), The toner is conveyed to the secondary transfer portion N2 by the registration roller 12. The registration roller 12 temporarily stops the conveyed sheet P, and supplies the sheet P to the secondary transfer portion N2 in synchronization with the toner image on the intermediate transfer belt 7 being conveyed to the secondary transfer portion N2. To do. In the conveyance direction of the sheet P, the next guide unit (conveyance guide) for regulating the conveyance path of the sheet P is disposed on the upstream side of the secondary transfer portion N2. First, on the surface side of the intermediate transfer belt 7, a secondary transfer upstream upper guide member 13 a that restricts the behavior of the sheet P approaching the surface of the intermediate transfer belt 7 is disposed. Further, a secondary transfer upstream lower guide member 13 b that restricts the behavior of the sheet P moving away from the surface side of the intermediate transfer belt 7 is disposed. The sheet P passes between the secondary transfer upstream upper guide member 13a and the secondary transfer upstream lower guide member 13b. That is, the conveyance path when the sheet P is conveyed from the registration roller 12 to the secondary transfer portion N2 is regulated by the secondary transfer upstream upper guide member 13a and the secondary transfer upstream lower guide member 13b.

  The toner image on the intermediate transfer belt 7 is nipped and conveyed between the intermediate transfer belt 7 and the secondary transfer belt 81 by the action of the secondary transfer device 11 in the secondary transfer portion N2. Above, electrostatic transfer (secondary transfer) is performed. At this time, a secondary transfer bias (secondary transfer voltage) having a polarity (positive in this embodiment) opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 82. As a result, a secondary transfer current is supplied to the secondary transfer portion N2. Deposits such as toner (secondary transfer residual toner) remaining on the intermediate transfer belt 7 after the secondary transfer process are removed from the intermediate transfer belt 7 by the intermediate transfer belt cleaner 74 and collected.

  The sheet P onto which the toner image has been transferred is separated from the intermediate transfer belt 7 and separated from the secondary transfer belt 81, and then conveyed to the fixing device 15 by the pre-fixing conveyance device 14. In this embodiment, the pre-fixing conveyance device 14 is a belt-type conveyance device, and adsorbs the lower surface of the sheet P with air so as not to disturb the toner transferred onto the sheet P and conveys the toner P to the fixing device 15. Then, after the unfixed toner image on the sheet P is fixed by the fixing device 15, the sheet P is discharged (output) outside the apparatus main body of the image forming apparatus 100.

2. Basic Configuration of Secondary Transfer Apparatus Next, the secondary transfer apparatus 11 in this embodiment will be described in more detail. Here, regarding the outer diameter of the endless belt tension roller, the central portion, the end portion, the entire region, etc., are regions where the belt is stretched in the rotation axis direction (longitudinal direction) of the tension roller (belt hung) Rotated area).

  The secondary transfer device 11 includes a belt unit 8, a cleaning unit 9, and a toner recovery unit 10.

  First, the belt unit 8 will be described. The belt unit 8 has a secondary transfer belt 81 formed of an endless belt. The secondary transfer belt 81 is stretched around a secondary transfer roller 82, a separation roller 83, a tension roller 84, and a driving roller 85 as a plurality of stretching rollers (support members). The secondary transfer roller 82 sandwiches the intermediate transfer belt 7 and the secondary transfer belt 81 between the secondary transfer counter roller 73 and forms a secondary transfer portion N2. The separation roller 83 separates the sheet P after passing through the secondary transfer portion N2 from the secondary transfer belt 81. The tension roller 84 is urged from the inner peripheral surface side to the outer peripheral surface side of the secondary transfer belt 81 by a spring (not shown) as an urging means, and applies tension (tension) to the secondary transfer belt 81. To do. The driving roller 85 transmits driving force from a driving motor (not shown) as driving means to the secondary transfer belt 81 to move (rotate) the secondary transfer belt 81. The secondary transfer belt 81 is rotationally driven by the driving roller 85 in the direction of the arrow R3 in the figure.

  The rollers are arranged in the order of the secondary transfer roller 82, the separation roller 83, the tension roller 84, and the drive roller 85 along the rotation direction of the secondary transfer belt 81. The secondary transfer roller 82, the separation roller 83, and the tension roller 84 are all driven and rotated as the secondary transfer belt 81 rotates. In this embodiment, the belt unit 8 is configured to be detachable from the secondary transfer device 11.

In this embodiment, the secondary transfer belt 81 is made of a resin such as polyimide or polycarbonate containing an appropriate amount of carbon black as an antistatic agent. The secondary transfer belt 81 has a volume resistivity of about 1 × 10 ⁹ to 1 × 10 ¹⁰ Ω · cm and a thickness of about 0.07 to 0.1 mm. In addition, the secondary transfer belt 81 used in this example is sufficiently hard with a Young's modulus value measured by a tensile test method (JIS K 6301) of about 100 MPa or more and 10 GPa or less.

In this embodiment, the secondary transfer roller 82 is configured by providing an elastic layer of ion conductive foamed rubber (NBR rubber) on a core metal (core material). The secondary transfer roller 82 has an outer diameter of 24 mm, a surface roughness Rz of 6.0 to 12.0 (μm), and an electrical resistance value of 2 kV in an N / N (23 ° C., 50% RH) environment. When applied and measured, it is 1 × 10 ⁵ to 1 × 10 ⁷ Ω. The elastic layer has an Asker-C hardness of about 30 to 40. The secondary transfer roller 82 is connected to a secondary transfer bias power source (high voltage power source) 87 as a secondary transfer bias applying unit. The supply bias of the secondary transfer bias power source 87 is variable, and a desired secondary transfer bias can be applied to the secondary transfer roller 82. By applying a secondary transfer bias to the secondary transfer roller 82, the toner image on the intermediate transfer belt 7 is transferred to the sheet P supplied to the secondary transfer portion N2, and the sheet is fed by the supplied electrostatic force. P is adsorbed to the secondary transfer belt 81. In this embodiment, for example, a secondary transfer bias is applied to the secondary transfer roller 82 so that a current of +40 to 60 μA flows.

  The secondary transfer belt 81 wound around the surface of the secondary transfer roller 82 moves in the direction of the arrow R3 in the figure, so that the sheet P adsorbed on the surface of the secondary transfer belt 81 at the secondary transfer portion N2 is obtained. Is conveyed downstream as indicated by arrow B in the figure. When the sheet P on the secondary transfer belt 81 reaches the position of the separation roller 83 disposed adjacent to the downstream of the secondary transfer roller 82 in the rotational direction of the secondary transfer belt 81, the curvature of the separation roller 83 is reached. Is separated from the surface of the secondary transfer belt 81. The sheet P separated from the secondary transfer belt 81 is conveyed to the fixing device 15 as described above.

  In the present embodiment, the separation roller 83 and the tension roller 84 are crown rollers having crown shapes in which the outer diameters of the central portion and the end portion in the rotation axis direction are different. Further, the secondary transfer roller 82 and the drive roller 85 each have a straight shape having substantially the same outer diameter in the entire area in the rotation axis direction. The separation roller 83 and the tension roller 84 will be described in more detail later.

  Next, the cleaning unit 9 will be described. The cleaning unit 9 includes a cleaning blade 91 and a fur roller 92 as cleaning members.

  The cleaning blade 91 is a plate-like member made of urethane rubber. The cleaning blade 91 is disposed in pressure contact with the outer peripheral surface of the secondary transfer belt 81 wound around the drive roller 85 with a predetermined contact angle and contact pressure. The fur roller 92 is configured by flocking nylon fibers onto a conductive roller. The fur roller 92 is disposed so as to be rotatable while maintaining an intrusion amount of about 1 mm with respect to the secondary transfer belt 81. Further, in this embodiment, a scraper shaft 93 made of a metal roller is disposed in contact with the fur roller 92.

  When the toner image is secondarily transferred onto the sheet P, the fur roller 92 rotates to rub the outer peripheral surface of the secondary transfer belt 81 to remove paper dust adhering to the secondary transfer belt 81. To do. The paper dust adhering to the fur roller 92 is scraped off by the scraper shaft 93. The cleaning blade 91 scrapes and removes toner adhering to the secondary transfer belt 81 from the outer peripheral surface of the rotating secondary transfer belt 81. Note that toner (fogging toner) or the like attached to the non-image area on the intermediate transfer belt 7 adheres to the secondary transfer belt 81 in the secondary transfer portion N2.

  The toner recovery unit 10 includes a recovery toner conveyance screw 10a. The toner collecting unit 10 collects the toner removed by the cleaning blade 91 together with the paper powder removed by the fur roller 92, and conveys (discharges) the toner to a waste toner box (not shown).

3. Separation Roller In this embodiment, as shown in FIG. 2A, the separation roller 83 is a regular crown roller having a regular crown shape in which the outer diameter of the central portion in the rotation axis direction is larger than the outer diameter of the end portion. ing. This is to suppress image defects (transfer defects) due to the corrugation of the sheet P. This will be described next.

  In general, a sheet P as a transfer body of a toner image, which is often paper, may be wavy for various reasons. For example, for paper that is wavy due to the influence of fixing processing (for example, when performing double-sided image formation), the length in the transport direction at the secondary transfer portion N2 is substantially perpendicular to the transport direction (hereinafter, “ In some cases, both ends are longer than the center in “width direction”.

  FIGS. 3A to 3C show the state of the vicinity of the secondary transfer portion N2 when the wavy paper is conveyed to the secondary transfer portion N2, as viewed from the secondary transfer belt 81 side. It is a schematic diagram (illustration of the secondary transfer belt 81 is omitted). When trying to affix the paper with undulations on the surface of the flat secondary transfer belt 81, as shown in FIG. 3 (a), an attempt is made to cancel the lengths of both ends in the width direction of the paper. The central portion in the width direction of the paper swells in a convex shape so as to be away from the secondary transfer belt 81. When the sheet having the center portion in the width direction swelled is transported to the secondary transfer portion N2 in that state, the center portion swells on the upstream side in the transport direction, as shown in FIG. If the bulge in the central portion cannot withstand the pressure of the secondary transfer portion N2, the bulge is crushed by the pressure of the secondary transfer portion N2, as shown in FIG.

  On the other hand, in this embodiment, the separation roller 83 disposed adjacent to the downstream of the secondary transfer roller (upstream roller) 82 in the rotation direction of the secondary transfer belt 81 is the normal crown roller as described above. Has been. Therefore, the separation roller 83 has a central portion in a direction substantially orthogonal to the rotation direction of the secondary transfer belt 81 (hereinafter also referred to as “width direction”) directed from the inner peripheral surface side to the outer peripheral surface side from the end portion. (Hereinafter, this direction is also referred to as “upward”). As a result, the surface of the secondary transfer belt 81 from the secondary transfer portion N2 to the position of the separation roller 83 has a shape in which the central portion in the width direction swells upward.

  As described above, in this embodiment, the paper is deformed so as to be convex upward on the downstream side of the secondary transfer portion N2, while the paper is sandwiched straight at the secondary transfer portion N2. In this state, the rigid body such as paper exerts a reaction force that becomes convex downward in the reverse direction between the portion deformed in a convex shape on the downstream side and the secondary transfer portion N2. . The force that causes the paper to protrude downward in the secondary transfer portion N2 reduces the bulge that causes wrinkles in the secondary transfer portion N2. For this reason, by using the separation roller 83 as a regular crown roller, it is possible to suppress wrinkles generated at the secondary transfer portion N2 in the sheet P on which undulation is generated.

  On the other hand, in this embodiment, as shown in FIG. 2B, the tension roller 84 is a reverse crown roller having a reverse crown shape in which the outer diameter of the central portion in the rotation axis direction is smaller than the outer diameter of the end portion. ing. The tension roller 84 is a stretching roller disposed adjacent to the downstream of the separation roller 83 in the rotation direction of the secondary transfer belt 81. That is, the separation roller 83 is a stretching roller (upstream roller) disposed adjacent to the upstream side of the tension roller 84 in the rotation direction of the secondary transfer belt 81. In the present embodiment, the tension roller 84 is a reverse crown roller in order to improve the effect of suppressing wrinkles of the sheet P by the separation roller 83 that is a normal crown roller. This will be described next.

  The effect of suppressing wrinkles of the sheet P by the regular crown roller as described above is obtained when the secondary transfer belt 81 that conveys the sheet P is sufficiently stretched along the shape of the regular crown roller. When the secondary transfer belt 81 is a belt made of a relatively hard material such as a resin belt, the secondary transfer belt 81 is not sufficiently deformed along the shape of the regular crown roller of the secondary transfer belt 81, and is effective in suppressing wrinkles. May be smaller.

  In contrast, in this embodiment, the tension roller 84 disposed adjacent to the downstream of the separation roller 83 in the rotation direction of the secondary transfer belt 81 is a reverse crown roller as described above. Therefore, the tension roller 84 deforms the end portion in the width direction of the secondary transfer belt 81 so as to protrude upward from the center portion. As a result, a force is applied to pull the secondary transfer belt 81 from the position of the separation roller 83 to the position of the tension roller 84 outward in the width direction. Therefore, even when the secondary transfer belt 81 is made of a relatively hard material as described above, the separation roller 83 causes the secondary transfer belt 81 to have a central portion in the width direction convex above the end portion. It becomes possible to stretch.

  Further, in this embodiment, the crown amount of the tension roller 84 is set equal to the crown amount of the separation roller 83 so that the circumferential length of the cross section of the secondary transfer belt 81 is substantially the same in the entire width direction of the secondary transfer belt 81. Is set. Thereby, the circumferential length of the secondary transfer belt 81 is prevented from remaining due to the position in the width direction, and the deflection of the secondary transfer belt 81 can be suppressed. Here, as shown in FIG. 2A, the maximum diameter (outer diameter of the central portion in the rotation axis direction) of the separation roller 83 is D1m, and the minimum diameter (outer diameter of the end portion in the rotation axis direction) is D1s. At this time, the crown amount of the separation roller 83 is represented by | D1s−D1m | / 2. As shown in FIG. 2B, when the minimum diameter of the tension roller 84 (the outer diameter of the central portion in the rotation axis direction) is D2m and the maximum diameter (the outer diameter of the end portion in the rotation axis direction) is D2s. The crown amount of the tension roller 84 is represented by | D2s−D2m | / 2.

4). Separation Mechanism Next, the separation mechanism of the sheet P from the secondary transfer belt 81 in this embodiment will be described.

  The sheet P separated from the secondary transfer belt 81 at the position of the separation roller 83 of the secondary transfer device 11 is then guided by the post-separation guide 20 as a guide member and delivered to the pre-fixing conveyance device 14. In this embodiment, a sheet conveying device 30 that conveys the sheet P is configured by including the belt unit 8 of the secondary transfer device 11 and the post-separation guide 20.

  In this embodiment, the toner adhering to the secondary transfer belt 81 is collected by the cleaning unit 9, so that a contact-type separation mechanism is not applied to the secondary transfer belt 81. Separation of the sheet P from the secondary transfer belt 81 is performed by the curvature of the separation roller 83. Then, the sheet P separated from the secondary transfer belt 81 is delivered to the post-separation guide 20 disposed in a non-contact manner with respect to the secondary transfer belt 81.

  The post-separation guide 20 is disposed close to the outer peripheral surface of the secondary transfer belt 81 wound around the separation roller 83 in a predetermined positional relationship described in detail below. As will be described in detail later, the post-separation guide 20 guides the sheet P at the center and both ends of the region through which the sheet P passes in the rotation axis direction of the separation roller 83 (hereinafter also referred to as “sheet passage region”). A central guide portion 20a and an end guide portion 20b (see FIG. 9). In this embodiment, the post-separation guide 20 is a single plate-like continuous member (flat plate) disposed along the rotation axis direction of the separation roller 83. In other words, in the present embodiment, the post-separation guide 20 is formed such that the center guide portion 20a and the end guide portion 20b are integrally formed so that the sheet P can be guided substantially throughout the sheet passing region. The length of the post-separation guide 20 in the rotation axis direction of the separation roller 83 is longer than the maximum length in the same direction of the sheet P used in the image forming apparatus 100. Then, the sheet P passes through a position from the center of the post-separation guide 20 in the rotation axis direction of the separation roller 83.

  Next, the positional relationship of the post-separation guide 20 with respect to the secondary transfer belt 81 will be described. Here, the rotation axis direction of the separation roller 83 (the width direction of the secondary transfer belt 81) may be referred to as “thrust direction”. Further, regarding the position of the post-separation guide 20 and the like, the vertical direction is the vertical direction in the gravity direction (vertical direction) in the normal use state of the image forming apparatus 100. However, the vertical direction does not mean only directly above or directly below, but includes being above and below a horizontal plane passing through a reference position or element.

  First, with reference to FIG. 4, the positional relationship of the post-separation guide 20 in the vertical direction (vertical direction) at the center in the thrust direction of the sheet passing region will be described.

  FIG. 4 is a schematic cross-sectional view in the vicinity of the separation of the sheet P from the secondary transfer belt 81, and a cross section (cross section approximately perpendicular to the thrust direction) in the center of the thrust direction of the sheet passing area is a thrust direction. It is what I saw. A broken line R in FIG. 4 indicates that the surface of the secondary transfer belt 81 (hereinafter also referred to as “conveying surface”) formed by the secondary transfer roller 82 and the separation roller 83 is downstream in the conveying direction B of the sheet P. This is a line extended toward the center (hereinafter also referred to as “central transport locus”). The transport surface is formed by stretching the secondary transfer belt 81 so that the sheet P is placed from above. A point A in FIG. 4 is a contact point (hereinafter, also referred to as “center contact point”) where the central transport locus R contacts the outer periphery of the separation roller 83. In the present embodiment, the position of the upstream end portion (hereinafter also referred to as “guide center front end”) F of the post-separation guide 20 in the conveyance direction of the sheet P is disposed below the central conveyance locus R. The reason is as follows.

  The sheet P is conveyed along the conveyance surface of the secondary transfer belt 81. After being separated from the secondary transfer belt 81, the sheet P is conveyed along the central conveyance locus R. However, the trajectory of the sheet P after being separated from the secondary transfer belt 81 may touch up and down the central transport trajectory R. For this reason, it is desirable that the position of the guide center front end F is on the lower side away from the central transport locus R.

Further, the sheet P receives gravity in the vertical direction after the leading end in the conveyance direction of the sheet P is separated from the secondary transfer belt 81 and reaches the post-separation guide 20. In particular, when the sheet P is a relatively small paper (thin paper) having a basis weight of 40 to 60 g / m ² , the leading edge of the sheet P is gradually curved downward. FIGS. 5A and 5B are views similar to FIG. 4 when the vertical position of the post-separation guide 20 is varied. As shown in FIG. 5A, when the guide center front end F is disposed below the central transport locus R, the front end of the sheet P after being separated from the secondary transfer belt 81 reaches the post-separation guide 20. When doing so, the orientation of the leading edge of the sheet P may be downward in the vertical direction. As a result, the angle formed by the direction of the leading edge of the sheet P (arrow E) and the conveying direction of the sheet P (arrow B) becomes a right angle or more, and the leading edge of the sheet P is rounded on the guide 20 after separation, resulting in poor conveyance. May occur. Therefore, as shown in FIG. 5B, from the central conveyance locus R, the front end of the sheet P reaches the post-separation guide 20 before the front end direction (arrow E) of the sheet P becomes downward in the vertical direction. It is desirable that the vertical distance to the guide 20 after separation is set to a predetermined value or less.

  Therefore, the vertical position of the guide center tip F is preferably set as follows. Here, a point C in FIG. 4 is a point indicating the rotation center of the separation roller 83 (hereinafter also referred to as “separation roller center”). Further, d in FIG. 4 indicates a distance from the above-described center contact A to the separation roller center C in the vertical direction. In addition, Zb in FIG. 4 indicates a distance from the center transport locus R to the guide center tip F in the vertical direction. At this time, the vertical position of the guide center tip F is preferably set so as to satisfy the relationship of Zb ≦ d. It is more preferable to satisfy the relationship of Zb <d. That is, the leading edge of the sheet P immediately after being separated from the secondary transfer belt 81 receives gravity and curves downward in the vertical direction. The smaller the basis weight of the sheet P, the greater the degree of curvature (curvature of curvature) with respect to the basis weight of the sheet P, which is closer to the curved state of the surface of the secondary transfer belt 81. However, even when the basis weight of the sheet P is relatively small, the curvature of curvature of the sheet P once separated from the secondary transfer belt 81 does not become larger than the curvature of curvature of the outer peripheral surface of the separation roller 83. Therefore, it is desirable that the position of the guide center tip end portion F is set at the same height as the separation roller center C or above the separation roller center C in the vertical direction. With such a setting, even when the basis weight of the sheet P is relatively small, the front end of the sheet P is moved before the direction of the front end of the sheet P becomes vertical downward with respect to the central transport path R in the vertical direction. The guide 20 is reached after separation.

  In the present embodiment, since the radius r of the central portion in the thrust direction of the separation roller 83 is 8 mm, the distance d from the central contact A to the separation roller center C in the vertical direction is 8 mm. In this embodiment, the distance Zb is 4.7 mm. Therefore, the relationship of Zb ≦ d (particularly Zb <d) is satisfied. However, the numerical values of d and Zb are not limited to the values in the present embodiment, and may be set so as to satisfy the relationship of Zb ≦ d (more preferably Zb <d).

  Next, the positional relationship related to the distance between the post-separation guide 20 and the secondary transfer belt 81 at the center in the thrust direction of the sheet passing area will be described.

  The further the guide center front end F is away from the separation roller 83, the easier the sheet P enters the gap between the post-separation guide 20 and the secondary transfer belt 81. If the guide center front end F is too close to the separation roller 83, the toner adhering to the secondary transfer belt 81 is likely to be transferred to the guide 20 after separation. From these viewpoints, in this embodiment, the guide center front end F is disposed at a position 1 mm away from the surface of the secondary transfer belt 81 on the straight line connecting the guide center front end F and the separation roller center C. As a result, it is possible to prevent the post-separation guide 20 from becoming dirty due to transfer of the toner adhering to the secondary transfer belt 81, and the sheet P is placed in the gap between the post-separation guide 20 and the secondary transfer belt 81. It is possible to suppress the catching.

  The positional relationship of the post-separation guide 20 described above is that in the central portion in the thrust direction of the sheet passing region, that is, in the central guide portion 20a. In the case where the separation roller 83 is a straight roller, good results can be obtained by having the above-described positional relationship in substantially the entire thrust direction of the sheet passing region. However, it has been found that when the separation roller 83 is a regular crown roller as in this embodiment, there are the following problems.

  FIG. 6 shows a case in which a normal crown roller is used as the separation roller 83 as a comparative example, and the post-separation guide 20 having substantially the same distance from the rotation axis of the separation roller 83 in almost the entire thrust direction of the sheet conveyance region. FIG. 5 is a schematic perspective view showing the vicinity of a separation roller 83. In FIG. 6, the secondary transfer belt 81 is not shown. When a regular crown roller is used as the separation roller 83, the sheet P is separated from the secondary transfer belt 81 at both ends earlier than the central portion in the thrust direction, and finally the central portion in the thrust direction is the secondary transfer belt 81. Separated from. At this time, in the sheet P separated from the secondary transfer belt 81, both end portions in the thrust direction hang down due to weight until the central portion in the thrust direction is separated. In this example, the gap between the secondary transfer belt 81 on the separation roller 83 that is a positive crown roller and the separated guide 20 is larger at both ends in the thrust direction of the sheet passing area than at the center. Therefore, the sheet P separated from the secondary transfer belt 81 is likely to be closer to the post-separation guide 20 at both ends in the thrust direction than at the center. In particular, with thin paper that is relatively weak, both ends in the thrust direction are likely to approach the post-separation guide 20 as described above. Become.

  Further description will be given with reference to FIGS. FIG. 7 is a schematic top view of the same configuration as FIG. 6 as viewed from above (the secondary transfer belt 81 is not shown), and FIG. 8 shows the same configuration as FIG. 6 in the thrust direction. It is the typical side view seen in. As in the present embodiment, the upstream end of the post-separation guide 20 in the transport direction of the sheet P at the central portion in the thrust direction of the sheet passing region is defined as a guide central front end F. Further, an end on the upstream side in the transport direction of the sheet P of the post-separation guide 20 at the end in the thrust direction of the sheet passing region is defined as a guide end front end F ′. As shown in FIG. 7, in this example, the upstream end of the post-separation guide 20 in the conveyance direction of the sheet P is substantially linear over substantially the entire area in the thrust direction of the sheet passing area. That is, the distance z between the guide center front end F and the separation roller center C and the distance z ′ between the guide end front end F ′ and the separation roller center C are substantially equal. In this case, the positional relationship of the post-separation guide 20 described above cannot be satisfied simultaneously at the center portion and the end portion of the sheet passing region (broken line P in the figure) in the thrust direction. In the present embodiment, the crown amount of the separation roller 83 is 1 to 3 mm. As in this embodiment, in this example, the distance x between the surface of the secondary transfer belt 81 and the guide center front end F is 1 mm. At this time, as shown in FIG. 8, the distance x ′ between the surface of the secondary transfer belt 81 and the guide end portion front end F ′ becomes larger than the distance x = 1 mm.

  Further, a broken line R ′ in FIG. 8 is a line (hereinafter referred to as “end”) that extends the conveyance surface of the secondary transfer belt 81 toward the downstream side in the conveyance direction B of the sheet P at the end in the thrust direction of the sheet passing region. Also referred to as “part transport trajectory”). Further, a point A ′ in FIG. 8 is a contact point at which the end conveyance locus R ′ contacts the outer periphery of the separation roller 83. Here, the end portion transport locus R ′ is positioned below the central transport locus R. The sheet P is conveyed along the end conveyance locus R ′ at the end in the thrust direction of the sheet passing area. Therefore, as shown in FIG. 8, if the guide center front end F and the guide end front end F ′ are arranged above the end portion transport locus R ′ (between R and R ′), the conveyance failure of the sheet P occurs. There is a fear. That is, at the end in the thrust direction of the sheet passing region, the sheet P cannot be landed on the guide 20 after separation and is easily caught.

  As described above, when the positional relationship of the post-separation guide 20 with respect to the central portion in the thrust direction of the sheet passing region is applied to substantially the entire region in the direction, when the separation roller 83 is a regular crown roller, the sheet P is separated. It may not be possible to prevent the guide 20 from being caught. Therefore, in this embodiment, the positional relationship of the post-separation guide 20 is as follows.

  FIG. 9 is a schematic top view of the vicinity of the separation roller 83 in this embodiment as viewed from above (the secondary transfer belt 81 is not shown), and FIG. 10 is a separation in this embodiment. It is the typical side view which looked at the neighborhood of roller 83 in the thrust direction.

  In the present embodiment, for the reasons described above, the guide center front end F and the guide end front end F ′ are both disposed below the central transport locus R in the vertical direction and have the same height as the separation roller center C or It is arranged above the separation roller center C. For the reason described above, the guide end tip F ′ is disposed below the end conveyance locus R ′ in the vertical direction and at the same height as the separation roller center C or above the separation roller center C. . In this embodiment, the post-separation guide 20 is formed of a flat plate that continues in the thrust direction. Therefore, in this embodiment, as shown in FIG. 10, both the guide center front end F and the guide end front end F ′ are disposed below the end transport locus R ′ in the vertical direction, and the center of the separation roller It is arranged at the same height as C or above the separation roller center C. Thereby, the sheet P separated from the secondary transfer belt 81 is more likely to land on the post-separation guide 20 over substantially the entire area in the thrust direction.

  Furthermore, in this embodiment, as shown in FIG. 9, the distance z ′ between the guide end tip F ′ and the separation roller center C is larger than the distance z between the guide center tip F and the separation roller center C. Is made smaller. Thus, in this embodiment, as shown in FIG. 10, the distance x between the surface of the secondary transfer belt 81 and the guide center front end F and the distance between the surface of the secondary transfer belt 81 and the guide end front end F ′. Are substantially equal, both of which are 1 mm. As a result, it is possible to suppress catching on the post-separation guide 20 due to sagging of the end portion in the thrust direction particularly in thin paper. The numerical values of the distances x and x ′ are not limited to the values in this embodiment, and the transfer of the toner adhering to the secondary transfer belt 81 to the post-separation guide 20 is sufficiently suppressed. From this point of view, it can be set appropriately. In this embodiment, the post-separation guide 20 is formed of a flat plate that continues in the thrust direction. Therefore, the distance between the upstream end of the pre-separation guide 20 in the sheet P conveyance direction and the separation roller center C gradually decreases from the guide center front end F to the guide end front end F ′. In particular, in the present embodiment, the upstream end of the pre-separation guide 20 in the conveyance direction of the sheet P is formed in a curved shape that is curved along the regular crown shape of the separation roller 83. As a result, the distance between the surface of the secondary transfer belt 81 and the upstream end of the post-separation guide 20 in the transport direction of the sheet P is made substantially equal over substantially the entire area in the thrust direction of the sheet passing area.

  As described above, in this embodiment, the guide member 20 includes the central guide portion 20a and the end guide portion 20b that guide the sheet P at the center portion and both end portions of the separation roller 83 in the rotation axis direction of the sheet. Have And in the cross section substantially orthogonal to the rotational axis of the separation roller 83, the upstream end F in the sheet P conveyance direction of the central guide portion 20a is arranged as follows. That is, the end portion F is below the tangent line of the belt 81 contacting the outer circumference of the upstream roller 82 and the outer circumference of the maximum diameter of the separation roller 83 and at the same height as the rotation center of the separation roller 83 or from the rotation center. Is also located above. Further, the upstream end F ′ in the conveyance direction of the sheet P of the end guide 20b is arranged as follows. That is, the end F ′ is below the tangent line of the belt 81 in contact with the outer periphery of the upstream roller 82 and the outer periphery of the minimum diameter of the separation roller 83 and at the same height as the rotation center of the separation roller 83 or the rotation center. It is located above. Further, the end on the upstream side in the conveyance direction of the sheet P of the end guide portion 20b is larger than the distance between the upstream end F in the conveyance direction of the sheet P of the central guide portion 20a and the rotation center of the separation roller 83. The distance between the portion F ′ and the rotation center of the separation roller 83 is smaller. In particular, in this embodiment, both the end portions F and F ′ are below the tangent line of the belt 81 contacting the outer periphery of the upstream roller 82 and the outer periphery of the minimum diameter of the separation roller 83 and the rotation of the separation roller 83. It is located at the same height as the center or above the center of rotation. In this embodiment, the guide member 20 is one continuous member disposed along the rotation axis direction of the separation roller 83, and in particular, a plate-like member having a surface on which a sheet is placed from above. .

  As described above, according to this embodiment, even if both ends in the thrust direction of the sheet P separated from the secondary transfer belt 81 hang down, the leading end in the transport direction of the sheet P can be more reliably received by the post-separation guide 20. it can. Thereby, the sheet P can be prevented from entering the gap between the secondary transfer belt 81 and the post-separation guide 20 and being caught by the post-separation guide 20, and jamming can be suppressed.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 11 is a schematic top view of the vicinity of the separation roller 83 in this embodiment as viewed from above (the secondary transfer belt 81 is not shown).

  In the first embodiment, the upstream end of the post-separation guide 20 in the conveyance direction of the sheet P has a curved shape along the regular crown shape of the separation roller 83. On the other hand, in the present embodiment, the upstream end of the post-separation guide 20 in the conveyance direction of the sheet P has a linear shape that is bent near the center in the thrust direction. That is, in this embodiment, the upstream end of the post-separation guide 20 in the transport direction of the sheet P has a plurality of linear portions connected by the bent portions. In particular, in this embodiment, two bent portions 20c and 20c are provided. The upstream end of the post-separation guide 20 in the conveyance direction of the sheet P is provided on the first straight portion 20d substantially parallel to the rotation axis of the separation roller 83 and on both ends of the first straight portion 20d. It has the 2nd linear part 20e and 20e. The second straight portion 20e is inclined with respect to the rotation axis of the separation roller 83 in the same direction as the surface of the separation roller 83 facing the second straight portion 20e.

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained, and simplification of molding can be expected as compared with the case where the end portion of the post-separation guide 20 is curved.

  In this embodiment, two bent portions are provided, but a configuration having one bent portion near the center in the thrust direction or a configuration having three or more bent portions may be used.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiment, the guide member is configured by a flat plate that is substantially uniform (flat) in the rotation axis direction of the separation roller. However, the present invention is not limited to this. The height of the upstream end of the guide member in the sheet conveyance direction may be different depending on the position of the separation roller in the rotation axis direction. For example, the height of the upstream end portion of the guide member in the sheet conveyance direction is gradually changed so that both end portions are lower than the central portion in the thrust direction, and when viewed in the sheet conveyance direction, It may be a convex V shape.

  In the above-described embodiment, the guide member is one member continuous in the rotation axis direction of the separation roller, and the distance between the upstream end of the guide member in the sheet conveyance direction and the rotation center of the separation roller. Was configured to change continuously. According to this configuration, regardless of the size in the thrust direction of the sheet that can be conveyed by the sheet conveying apparatus, the above-described distance relationship can be satisfied at the central portion and the end portion in the thrust direction for each size sheet. That is, the portion that guides the central portion of each size sheet can be regarded as the central guide portion, and the portion that guides the end portion can be regarded as the end guide portion. However, the present invention is not limited to this. For example, when the size in the thrust direction of the sheet conveyed by the sheet conveying apparatus is fixed to a predetermined size, the guide portions that respectively guide the central portion and the end portion of the predetermined size sheet in the thrust direction. May be separated. Similarly, when the height of the upstream end portion of the guide member in the sheet conveyance direction is varied depending on the position of the separation roller in the rotation axis direction as described above, the height is continuously varied. The above-mentioned height relationship can be satisfied even for a sheet of the size. However, it is not limited to this, The guide part of each height may be isolate | separated.

  In the above-described embodiments, the present invention is applied to the belt that conveys the sheet at the secondary transfer unit that transfers the toner image from the intermediate transfer member to the sheet as the image carrier (second image carrier). However, the present invention is not limited to this. For example, the present invention can be applied to a belt that conveys a sheet by a transfer unit that transfers a toner image directly from a photosensitive drum as an image carrier to the sheet, and the same effects as in the above-described embodiments can be obtained. .

1 Photosensitive drum 7 Intermediate transfer belt 8 Belt unit 11 Secondary transfer device 20 Guide after separation (guide member)
30 Sheet conveying device 81 Secondary transfer belt 83 Separation roller

Claims (11)

A rotatable endless belt carrying and transporting a sheet;
A plurality of stretching rollers for stretching the belt, the upstream roller disposed on the upstream side in the rotational direction of the belt, forming a surface of the belt stretched so that a sheet is placed from above; and A plurality of stretching rollers including a separation roller disposed downstream in the rotational direction of the belt and separating the sheet from the belt;
A guide member arranged in a non-contact manner with respect to the belt, for guiding a sheet separated and conveyed from the belt;
Have
In the sheet conveying apparatus, the separation roller is a positive crown roller having a positive crown shape in which the outer diameter of the central portion in the rotation axis direction is larger than the outer diameter of the end portion.
The guide member has a central guide portion that guides the sheet at both ends of the central portion of the region where the sheet passes in the rotational axis direction of the separation roller, and an end guide portion, respectively.
In a cross-section substantially orthogonal to the rotation axis of the separation roller, an upstream end in the sheet conveyance direction of the central guide portion has an outer periphery of the upstream roller and an outer periphery of the maximum diameter of the separation roller. It is located below the tangential line and at the same height as the rotation center of the separation roller or above the rotation center, and the upstream end portion of the end guide portion in the sheet conveying direction is the upstream roller. Located below the belt tangent to the outer periphery and the outer periphery of the smallest diameter of the separation roller, and at the same height as the rotation center of the separation roller or above the rotation center,
More than the distance between the upstream end in the sheet conveying direction of the central guide portion and the rotation center of the separation roller, the upstream end in the sheet conveying direction of the end guide portion and the separating roller A sheet conveying apparatus having a smaller distance from the rotation center of the sheet.   In the cross section substantially orthogonal to the rotation axis of the separation roller, the upstream end in the sheet conveyance direction of the center guide portion and the end guide portion is the outer periphery of the upstream roller and the outer periphery of the minimum diameter of the separation roller. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is located below a tangent line of the belt in contact with the belt and at the same height as the rotation center of the separation roller or above the rotation center.   The guide member is one continuous member arranged along the rotation axis direction of the separation roller, and is located between the upstream end of the guide member in the sheet conveyance direction and the rotation center of the separation roller. The sheet conveying apparatus according to claim 1, wherein the distance is gradually decreased from the central guide portion to the end guide portion.   The sheet conveying apparatus according to claim 3, wherein an upstream end portion of the guide member in a sheet conveying direction is formed in a curved shape along a regular crown shape of the separation roller.   The sheet conveying apparatus according to claim 3, wherein an upstream end portion of the guide member in the sheet conveying direction has a plurality of linear portions connected by a bent portion.   The sheet conveying apparatus according to claim 3, wherein the guide member is a plate-like member having a surface on which a sheet is placed from above.   Among the plurality of stretching rollers, the stretching roller provided adjacent to the downstream side of the separation roller in the rotation direction of the belt is a tension roller that applies tension to the belt, and the tension roller is The sheet conveying device according to any one of claims 1 to 6, wherein the sheet conveying device is a reverse crown roller having a reverse crown shape in which an outer diameter of a central portion in a rotation axis direction is smaller than an outer diameter of an end portion.   The sheet conveying device according to any one of claims 1 to 7, wherein the belt is a resin belt.   An image forming apparatus for forming an image with toner on a sheet, comprising the sheet conveying device according to claim 1.   An image carrier that carries a toner image, and the upstream roller contacts the image carrier via the belt and is conveyed between the image carrier and the belt. The image forming apparatus according to claim 9, wherein a transfer portion that transfers toner from the image carrier is formed.   A power source for applying a voltage to the upstream roller, and a voltage is applied to the upstream roller so that the sheet is attracted to the belt and a toner image is transferred from the image carrier to the sheet. The image forming apparatus according to claim 10.

Images