JP5627282B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet conveying apparatus having an improved sheet conveying structure in a guide plate having ribs, and an image forming apparatus including the sheet conveying apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus, in order to convey a sheet on which an image is formed, a conveyance path is formed and guided using a pair of guide plates that guide both front and back surfaces of the sheet. The guide plate is configured by combining a flat portion, a bent portion, a curved portion, and the like in the image forming apparatus main body provided with a conveyance path for guiding both the front and back sides of the sheet.

  In recent years, with the increasing needs of image forming apparatuses, the types of sheets that are conveyed have increased compared to the conventional ones. In particular, when transporting coated paper or thin sheets, the contact between the sheet and the guide increases, causing sticking of the sheet to the guide plate, or increasing the sheet transport resistance and causing a transport failure. May cause problems.

  Further, regarding the guide plate downstream of the fixing device, in the case of a sheet type such as coated paper or thin sheet, it may stick to the guide plate due to condensation or static electricity, and jamming may occur. For this reason, in order to prevent sticking, a rib is generally provided in the sheet conveyance region of the guide plate, and sticking is prevented by reducing the contact area between the sheet and the guide by the rib.

  However, in the case of the above configuration, when a thick sheet is conveyed, contact resistance increases when it comes into contact with the rib, and the image formed on the sheet has traces of the rib, or the leading edge of the sheet hits the rib. There is a risk that the end of the sheet may be damaged.

  Therefore, ribs are arranged at a predetermined angle with respect to the sheet conveyance direction at the curved portion of the conveyance guide to reduce the rubbing by preventing the contact between the conveyance guide and the sheet from being concentrated on a part of the width direction. There has been proposed an apparatus having a configuration in which the above-mentioned is reduced. (See Patent Document 1)

  In this apparatus, a sheet conveying unit that conveys a sheet and a guide unit that guides a sheet conveyed by the sheet conveying unit are provided in the sheet conveying apparatus, and the guide unit is curved with respect to the conveying direction of the sheet to be conveyed. And a straight portion. The guide part is provided with a rib that contacts the sheet over the curved part and the straight part. The rib is disposed at a predetermined angle with respect to the sheet conveyance direction at the curved portion, and at least a part of the straight portion is disposed at an angle parallel to or smaller than the predetermined angle with respect to the sheet conveyance direction. Thereby, it is possible to reduce the damage to the sheet due to the friction between the sheet and the rib at the curved portion, and the damage to the sheet due to the starting point of the rib.

JP 2009-286552 A

  However, in the technique described in Patent Document 1, since the height of the rib of the guide portion is uniform at the curved portion, there is a possibility that strong rubbing occurs between the rib of the inner guide portion at the curved portion and the sheet. there were. Especially during double-sided image formation (double-sided printing) or face-down (when the imaged surface is transported in a downward state), the image that contacts the ribs on the inner guide is rubbed strongly, and the rubbed part is There is a risk that gloss difference and gloss unevenness may occur due to the difference in gloss.

  Accordingly, the present invention provides a sheet conveying apparatus capable of suppressing the glossy streaks and gloss unevenness of an image due to strong rubbing particularly during double-sided image formation or face down, and an image forming apparatus equipped with the sheet conveying apparatus. The purpose is to do.

The present invention provides a sheet conveying apparatus having a guide member having a flat guide section and the curved guide portion which is formed continuously, the guide member, the protruding ribs extending along the sheet conveying direction, the flat guide parts and protrudes from the guide surface of the curved guide section is formed by Uni continuously by contacting the sheet to be conveyed, the protruding rib, which has a gradually expanding shape toward the rib top to the guide surface , the sheet length in the conveying direction and a width direction perpendicular rib top of a curved guide portion, wherein than the length of the width direction of the rib top of the flat guide portion is configured to become longer so, the The protrusion amount of the rib top portion from the guide surface at the curved guide portion is smaller than the protrusion amount of the rib top portion from the guide surface at the flat guide portion .

  In the present invention, “extending along the sheet conveying direction” not only means extending in parallel to the sheet conveying direction, but also means extending roughly along the sheet conveying direction. It is a concept that also includes

According to the present invention, the projecting rib, the length in the width direction of the rib apex in the curved guide section is configured to be become longer so than the length in the width direction of the rib top of the flat guide portion. For this reason , since the contact pressure between the protruding rib and the sheet in the curved guide portion can be reduced, it is possible to suppress gloss streaks and uneven gloss of the image due to strong rubbing particularly during double-sided image formation (double-sided printing). Thereby, the sheet conveying apparatus corresponding to a high range of sheet types can be provided.

FIG. 3 is a side view showing the configuration of the sheet conveying apparatus according to the first embodiment of the present invention. (A) is a perspective view which shows the conveyance guide plate in the sheet conveying apparatus of 1st Embodiment, (b) is a perspective view which expands and shows a part of rib in (a), (c) is (a). The top view which shows a conveyance guide plate. (A) is a side view showing a conveyance guide plate in the sheet conveying apparatus of the first embodiment, and (b) is a side view showing a part of a rib in (a) in an enlarged manner. (A) is a figure which shows the conveyance guide plate in the sheet conveyance apparatus of 1st Embodiment in the state seen from the sheet conveyance direction downstream, (b) is sectional drawing which expands and shows a part of rib in (a). . (A) is a perspective view which shows the conveyance guide plate of the flat state in the preparation process in 1st Embodiment, (b) is a perspective view which expands and shows a part of rib in (a), (c) is ( The top view which shows the conveyance guide plate of a). (A) is a side view which shows the conveyance guide plate of the flat plate state in FIG. 5, (b) is a side view which expands and shows a part of rib in (a). 5A is a perspective view showing a state in which a recess is formed in the flat conveyance guide plate in FIG. 5, FIG. 5B is a perspective view showing a part of the rib in FIG. 5A enlarged, and FIG. The top view which shows the conveyance guide plate of). (A) is a side view which shows the conveyance guide plate in which the recessed part in FIG. 7 was formed, (b) is a side view which expands and shows a part of rib in (a). The side view which shows the structure of the sheet conveying apparatus of 2nd Embodiment which concerns on this invention. (A) is a perspective view which shows the conveyance guide plate in the sheet conveying apparatus of 2nd Embodiment, (b) is a perspective view which expands and shows a part of rib in (a), (c) is (a). The top view which shows a conveyance guide plate. (A) is a side view which shows the conveyance guide plate in the sheet conveying apparatus of 2nd Embodiment, (b) is a side view which expands and shows a part of rib in (a). (A) is a figure which shows the conveyance guide plate in the sheet conveyance apparatus of 2nd Embodiment in the state seen from the sheet conveyance direction downstream, (b) is sectional drawing which expands and shows a part of rib in (a). . Sectional drawing which shows the color image forming apparatus in 1st and 2nd embodiment. (A) is a perspective view which shows the bending conveyance guide plate in a comparative example, (b) is a perspective view which expands and shows a part of rib in (a). (A) is a top view which shows the bending conveyance guide plate in a comparative example, (b) is a side view which shows the conveyance guide plate of (a), (c) is a perspective view which expands and shows a part of rib in (a). Figure. (A) is a figure which shows the state which looked at the bending conveyance guide plate in a comparative example from the sheet conveyance direction downstream, (b) is sectional drawing which expands and shows a part of rib in (a). (A) is a perspective view which shows the curved conveyance guide plate in a comparative example, (b) is a perspective view which expands and shows a part of rib in (a). (A) is a top view which shows the curved conveyance guide plate in a comparative example, (b) is a side view which shows the curved conveyance guide plate of (a), (c) expands and shows a part of rib in (a). Perspective view. (A) is a figure which shows the curved conveyance guide plate in a comparative example in the state seen from the sheet conveyance direction downstream, (b) is sectional drawing which expands and shows a part of rib in (a).

<First Embodiment>
Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. First, an image forming apparatus provided with a sheet conveying apparatus to which the present invention is applied will be described with reference to FIG. FIG. 13 is a cross-sectional view of an intermediate transfer tandem color image forming apparatus 60 which is an image forming apparatus according to the present invention.

  As shown in FIG. 13, the sheet S is stored in a form of being stacked on a lift-up mechanism 42 included in a feeding storage 41 that is a sheet stacking unit, and an image of the image forming mechanism 40 is fed by a feeding roller 43. It is sent out according to the formation timing.

  The sheet S sent out by the feeding roller 43 is subjected to skew correction in the active registration unit 45, then passes through the transport unit 44 and is sent to the secondary transfer unit. The secondary transfer portion is a toner image transfer nip portion to the sheet S formed by the substantially opposite secondary transfer inner roller 403 and the secondary transfer outer roller 46, and has a predetermined pressure and an electrostatic additional bias. Is applied, the unfixed image is adsorbed on the sheet surface.

  The conveyance path for conveying the sheet S is a sheet conveyance mechanism (for example, a roller pair or a suction belt) arranged at an appropriate interval for holding the sheet S and holding the sheet S, while suppressing the behavior of the sheet S. And a guide for guiding.

  A process of forming an image sent to the secondary transfer unit at the same timing as the conveyance process of the sheet S to the secondary transfer unit described above will be described.

  An image forming unit 413 for forming an image on a sheet mainly includes a photosensitive drum 408, an exposure device 411, a developing device 410, a primary transfer mechanism 407, and a photosensitive cleaner 409. An exposure device 411 emits light based on a signal of image information sent to a photosensitive drum 408 rotated in the direction of arrow A in the figure, the surface of which is uniformly charged in advance by a charging device (not shown). An electrostatic latent image is formed through the diffraction unit 412 and the like as appropriate.

  In this way, toner development by the developing device 410 is performed on the electrostatic latent image formed on the photosensitive drum 408, and a toner image is formed on the photosensitive drum. Thereafter, a predetermined pressing force and an electrostatic additional bias are applied by the primary transfer mechanism 407, and the toner image is transferred onto the intermediate transfer belt 406. Thereafter, the transfer residual toner slightly remaining on the photoconductor drum 408 is collected by the photoconductor cleaner 409, and prepared for the next image formation again.

  In the case of FIG. 13, the image forming unit 413 described above has four sets of yellow (Y), magenta (M), cyan (C), and black (Bk). Of course, it is not limited to four colors, and the order of colors is not limited to this.

  Next, the intermediate transfer belt 406 will be described. The intermediate transfer belt 406 is stretched by rollers such as a driving roller 404, a tension roller 405, and a secondary transfer inner roller 403, and is conveyed and driven in the direction of arrow B in the drawing. Therefore, the image forming process of each color that is processed in parallel by the Y, M, C, and Bk image forming units 413 described above is performed at the timing at which the upstream toner image that has been primarily transferred onto the intermediate transfer belt is superimposed. . As a result, a full-color toner image is finally formed on the intermediate transfer belt 406 and conveyed to the secondary transfer unit.

  As described above, the full-color toner image is intermediately transferred onto the sheet S in the secondary transfer portion by the sheet conveying process and the image forming process described above. Thereafter, the sheet S is conveyed from the pre-fixing conveyance unit 47 to the fixing unit 48, and the toner image is dissolved and fixed by a device such as pressurization and heating. The sheet S having a fixed image obtained in this way is discharged as it is onto the discharge tray 400 by the branch transfer mechanism 49 (sheet transfer device 100 described later). Alternatively, when double-sided image formation (double-sided printing) is required, a route selection as to whether or not the reverse conveyance mechanism 401 is conveyed to the double-sided conveyance mechanism 402 is performed.

  During the double-sided printing, the sheet S on which the image is fixed on the first surface (front surface) by the fixing unit 48 is sent to the reverse conveyance mechanism 401 side, reversed upside down, and sent to the double-side conveyance mechanism 402. Then, the sheet S is synchronized with the sheet S sent out from the feeding storage 41 by the feeding roller 43 in synchronization with the fixing unit via the active registration unit 45, the transport unit 44, the secondary transfer unit, and the pre-fixing transport unit 47. 48. Further, the image of the sheet S is fixed on the second surface (back surface), and then discharged onto the paper discharge tray 400 via a sheet conveying device 100 described later.

  Next, a first embodiment according to the present invention will be described with reference to FIGS. A sheet conveying apparatus 100 shown in FIG. 1 is arranged at a position indicated by reference numeral 500 in FIG.

  As shown in FIG. 1, a sheet conveying apparatus 100 that conveys an image-formed sheet has an upper conveying guide plate between an upstream conveying roller 101 (101a, 101b) and a downstream conveying roller 102 (102a, 102b). 103 and the lower conveyance guide plate 220 are arranged. The sheet conveying apparatus 100 includes an upper conveying guide plate 103 positioned on the curved outer side and a lower conveying guide plate 220 positioned on the curved inner side. The lower conveyance guide plate 220 constitutes a guide member having a flat guide portion 200a and a curved guide portion 200b formed continuously. The lower conveyance guide plate 220 serving as a guide member is disposed downstream in the sheet conveyance direction from the fixing unit 48 that fixes the toner image formed on the sheet S in the image forming unit 413.

  The sheet conveying apparatus 100 including the upper conveying guide plate 103 and the lower conveying guide plate 220 is disposed at a position indicated by reference numeral 500 in FIG. 13 in the image forming apparatus main body. The upper conveyance guide plate 103 and the lower conveyance guide plate 220 are configured to convey the sheet S that has passed through the fixing unit 48 along an obliquely upward direction.

  In the sheet conveying apparatus 100, a gap between the guide plates at a predetermined interval between the upper conveying guide plate 103 and the lower conveying guide plate 220 is strictly defined in order to cope with a high range of sheet types. In the sheet conveying apparatus 100, the processing accuracy is improved by providing the lower conveying guide plate 220 with guide ribs 221 to 228 which are a plurality of protruding ribs in the shape of the conveying path conveyed upward.

  The lower conveyance guide plate 220, which is a guide member, has guide ribs 221 to 228 extending along the sheet conveyance direction (arrow A direction) so as to come into contact with the sheet conveyed protruding from the outer guide surface 220b of the curved guide portion 200b. It is formed continuously with the flat guide part 200a. The phrase “extending along the sheet conveying direction” includes not only the meaning of extending in parallel with the sheet conveying direction but also the meaning of extending approximately along the sheet conveying direction. It is a concept. These guide ribs (projecting ribs) 221 to 228 are integrally formed with the lower conveyance guide plate 220. The guide ribs 221 to 228 and the lower conveyance guide plate 220 can be made of sheet metal.

  The lower conveyance guide plate 220 as a guide member is located downstream of the fixing unit 48, and when conveying coated paper or a thin sheet, sticking occurs in the lower conveyance guide plate 220 due to condensation or static electricity, and a jam occurs. May occur. Therefore, in the present embodiment, guide ribs 221 to 228 for preventing sticking are provided, and the contact area between the sheet S and the lower transport guide plate 220 is reduced by the guide ribs 221 to 228 to prevent sticking. . Further, by forming a curved portion (bent portion) in the lower conveyance guide plate 220, the contact pressure concentration between the sheet S and the guide ribs 221 to 228 is reduced.

  In this embodiment, in order to reduce damage to the sheet S, the arrangement of the guide ribs 221 to 228 is formed so as to expand as it proceeds downstream (upper left in FIG. 1) (see FIG. 2). . That is, the guide ribs 221 to 228 are arranged so as to spread outward from the center in the width direction orthogonal to the sheet conveying direction toward the downstream side in the sheet conveying direction. Thereby, the contact in the same location with the guide ribs 221-228 and the sheet | seat S is avoided, and the image flaw of the sheet | seat S is prevented.

  Further, the guide ribs 221 to 228 are configured such that the contact area with the sheet S at the curved guide part 200 b having the bent part is larger than the contact area with the sheet S at the flat guide part 200 a of the lower conveyance guide plate 220. Is formed.

  An upstream-side conveyance roller 101 (101a, 101b) and a downstream-side conveyance roller 102 (102a, 102b) serving as a conveyance unit that conveys a sheet to the upstream side and the downstream side in the sheet conveyance direction of the lower conveyance guide plate 220 that is a guide member. ). The conveyance speed of the downstream conveyance roller 102 on the downstream side is higher than the conveyance speed of the upstream conveyance roller 101 on the upstream side. That is, in order to prevent scratches on the image surface side of the sheet S that has passed through the fixing unit 48, the number of rotations of the downstream side conveyance roller 102 shown in FIG. 1 is set to be faster than that of the upstream side conveyance roller 101. Therefore, the sheet is conveyed in a tension system. Accordingly, since the sheet S is conveyed along the lower conveyance guide plate 220, sliding (sliding contact) between the image surface and the upper conveyance guide plate 103 is prevented, and image scratches (rubbing on the image surface side) are prevented. Generation of scratches is prevented.

  In the lower conveyance guide plate 220 (see FIGS. 2 to 4) having a characteristic configuration as a guide member in the present embodiment, for example, the rib height 230 (FIG. 4B) of the bent portion of the guide rib 221 is changed to the bent portion. Other than the rib height 231 (FIG. 4 (b)), it is formed lower. In the guide ribs (protruding ribs) 221 to 228 in the curved guide portion 200b, the protrusion amount of the rib top portion from the outer guide surface 220b is smaller than the protrusion amount of the rib top portion from the guide surface 220a of the flat guide portion 200a. That is, the guide ribs (protruding ribs) 221 to 228 of the curved guide portion 200b of the lower conveyance guide plate 220 have a protruding amount (rib height 230) from the outer guide surface 220b to the top of the rib, and the guide surface 220a of the flat guide portion 200a. It is lower than the protruding amount from the rib top. And the large area part with a large contact area with the sheet | seat conveyed is formed in the rib top part of these guide ribs 221-228, respectively. Since the guide ribs 221 to 228 are formed so as to gradually spread from the rib top toward the guide surface, the area where the rib is lowered by a press or the like has a larger contact area than the other ribs, A wide area portion is formed. The same applies to the second embodiment described later.

  This wide area part (part where the protrusion amount of the rib top part is small) is the wide area part 221a in the guide rib 221, and the same large area parts 221b, 221c, 221d are the wide area part 221a upstream in the sheet conveying direction. A plurality of them are provided at a predetermined distance from the downstream to the downstream. A wide area portion is also formed on the rib tops of the other guide ribs 222 to 228 so as to be in the same state as this. Thus, the wide area part formed in the rib top part of the bending part with low rib height is based on the construction method which forms a guide rib in the lower conveyance guide plate 220 which consists of sheet metal by press work so that it may mention later. By suppressing the protrusion amount from the guide surface to the rib top at the bent portion, the radius of curvature of the bent portion can be increased, and the contact pressure with the conveying sheet at the bent portion of the guide rib can be reduced.

  In the sheet conveying apparatus 100, as described above, since the sheet is conveyed in the pulling system in order to prevent the rubbing scratch on the image surface side, the lower conveying guide without the setting of the rib top protrusion amount as described above. The following inconveniences that occur in the case of the plate 200 do not occur. That is, when a thick and highly glossy sheet is conveyed, in the lower conveyance guide plate 200 with no rib top protrusion amount setting shown in FIGS. 14 to 16 as a comparative example, the sheet S is formed at the bent portion 201a of the guide rib 201. Is strongly rubbed, and the gloss of the rubbed portion is lowered. Thereby, the gloss streak is visually recognized over the entire surface of the sheet S in the conveyance direction. In addition, the code | symbol 210 of Fig.16 (a) is a rib height, and the codes | symbols 202-208 in Fig.15 (a) are the guide ribs similar to the guide rib 201. FIG. Reference numerals 201b, 201c, and 201d in FIG. 15B are bent portions similar to the bent portion 201a in FIG. In the present embodiment, when the curved guide portion 200b is formed on the lower conveyance guide plate 220 made of sheet metal, a curved guide portion is formed as a whole by bending at a plurality of locations by press working. Also, in the lower conveyance guide plate 310 in which the rib top protrusion amount is not set as shown in FIGS. 17 to 19 as another comparative example, the sheet S is strongly rubbed by the bent portion 201a of the guide rib 311. The gloss of the is reduced. Thereby, the gloss streak is visually recognized over the entire surface of the sheet S in the conveyance direction. In FIG. 19B, reference numeral 320 denotes a rib height, and reference numerals 312 to 318 in FIG. 18A denote guide ribs similar to the guide rib 311.

  In order to prevent the above inconvenience, in this embodiment, a rib height 231 other than the wide area portion 221a is formed lower than a wide area portion 221a, such as a wide area portion 221a formed in a bent portion of the guide rib 221 shown in FIGS. The contact area to the seat is increased. Except the wide area part 221a means the guide ribs 221 to 228 in the flat guide part 200a. Accordingly, the rib height 230 of the wide area portion 221a is lowered without changing the rib height 231 other than the wide area portion 221a of the bent portion, while reducing the contact pressure with the sheet S and preventing the occurrence of gloss streaks. Thus, the function of preventing the sheet S from sticking is maintained.

  Here, a method of forming the large area portions 221a to 221d and the like with respect to the lower conveyance guide plate 220 before processing in the present embodiment will be described.

  The lower conveyance guide plate 220 is formed of a SUS plate material and is manufactured by a press method. As shown in FIGS. 5A to 5C and FIGS. 6A and 6B, first, the outer shape of the lower conveyance guide plate 250 is imitated, and the guide rib 221 is formed before the wide area portions 221a to 221d are formed. Prototype shape is produced. Thereby, the lower conveyance guide plate 220 and the guide rib 221 are formed as shown in FIG. The same applies to the other guide ribs 222 to 228.

  After the above steps, as shown in FIGS. 7A and 7B and FIGS. 8A and 8B, a portion where the large area portions 221a to 221d are formed is previously pressed from the protruding side of the guide rib 221. And make these parts lower than other parts. Thereafter, as shown in FIGS. 3A and 3B, the lower formation portion is stretched by bending at the formation portion of the plurality of wide area portions that are lowered by one step on the guide rib 221, so as to extend from the other portions. Are also formed as wide area portions 221a to 221d having a step shape that is one step lower.

  Of course, the above description shows an example of the guide plate fabrication, and the material and the formation method are not limited to this. For example, even in a guide plate formed of a resin mold of a different material, it is possible to form a wide area portion with a rib height kept low at a bent portion. Also, in the construction methods other than the sheet metal press construction method, a rib having a taper-shaped cross section in a direction orthogonal to the sheet conveying direction formed at a uniform height is ground at the top of the bent portion in the subsequent process. Anyway.

  According to the above-described embodiment, the guide ribs 221 to 228 extending along the sheet conveyance direction so as to contact the sheet conveyed while protruding from the outer guide surface 220b of the curved guide part 200b are continuous with the flat guide part 200a. Is formed. The guide ribs 221 to 228 are formed such that the contact area to the sheet at the curved guide portion 200b is larger than the contact area to the sheet at the flat guide portion 200a of the lower conveyance guide plate 220. Thereby, the contact pressure between the guide ribs 221 to 228 and the sheet S in the curved guide portion 200b of the lower conveyance guide plate 220 can be reduced. Accordingly, it is possible to suppress gloss streaks and gloss unevenness of the image forming surface due to strong rubbing particularly during double-sided printing or face-down, and to provide a sheet conveying apparatus 100 corresponding to a wide range of sheet types. it can.

<Second Embodiment>
Next, a second embodiment according to the present invention will be described with reference to FIGS. Note that the basic configuration of the apparatus of the present embodiment is the same as that of the first embodiment described above, and therefore, a duplicate description is omitted. Here, a configuration that is a feature of the present embodiment will be described.

  The sheet conveying apparatus 300 shown in FIG. 9 in the present embodiment is also arranged at a position indicated by reference numeral 500 in FIG. 13 on the downstream side in the sheet conveying direction from the fixing unit 48 in the image forming apparatus main body.

  As shown in FIG. 9, the sheet conveying apparatus 300 includes an upper conveying guide plate 303 and a lower conveying guide plate 304 between the upstream conveying rollers 301 (301a and 301b) and the downstream conveying rollers 302 (302a and 302b). Is arranged. The lower conveyance guide plate 304 constitutes a guide member having a flat guide portion 301a and a curved guide portion 301b formed continuously.

  The sheet conveying apparatus 300 including the upper conveying guide plate 303 and the lower conveying guide plate 304 is disposed at a position indicated by reference numeral 500 in FIG. 13 in the image forming apparatus main body. The upper conveyance guide plate 303 and the lower conveyance guide plate 304 are configured to convey the sheet S that has passed through the fixing unit 48 along an obliquely upward direction.

  The lower conveyance guide plate 304 is located downstream of the fixing unit 48. When the coated paper or the thin sheet is conveyed, the lower conveyance guide plate 304 may stick to the lower conveyance guide plate 304 due to condensation or static electricity. There is. Therefore, as shown in FIGS. 10 and 11, guide ribs (projecting ribs) 351 to 358 for preventing sticking are provided, and the contact area between the sheet S and the lower conveyance guide plate 304 is reduced by the guide ribs 351 to 358. Therefore, sticking is prevented. Further, by forming a curved portion in the lower conveyance guide plate 304, contact pressure concentration between the sheet S and the guide ribs 351 to 358 is prevented.

  In the present embodiment, in order to reduce damage to the sheet S, the arrangement of the guide ribs 351 to 358 is formed so as to expand as it proceeds downstream (upper left in FIG. 9) (see FIG. 10). . That is, the guide ribs 351 to 358 are arranged so as to spread outward from the center in the width direction orthogonal to the sheet conveyance direction toward the downstream in the sheet conveyance direction. Thereby, the contact in the same location with the guide ribs 351-358 and the sheet | seat S is avoided, and the image flaw of the sheet | seat S is prevented.

  Further, the guide ribs 351 to 358 are formed so that the contact area to the sheet S at the curved guide portion 301b is larger than the contact area to the sheet S at the flat guide portion 301a of the lower conveyance guide plate 304. Yes.

  Also in this embodiment, an upstream side conveyance roller 301 (301a, 301b) and a downstream side conveyance roller 302 (302a, 302b) serving as a conveyance unit that conveys a sheet to the upstream side and the downstream side in the sheet conveyance direction of the lower conveyance guide plate 304. 302b). The conveyance speed of the downstream conveyance roller 302 on the downstream side is higher than the conveyance speed of the upstream conveyance roller 301 on the upstream side. That is, in order to prevent scratches on the image surface side of the sheet S that has passed through the fixing unit 48, the rotational speed of the downstream side conveyance roller 302 shown in FIG. 9 is set to be faster than that of the upstream side conveyance roller 301. Therefore, the sheet is conveyed in a tension system. Accordingly, since the sheet S is conveyed along the lower conveyance guide plate 304, sliding (sliding contact) between the image surface and the upper conveyance guide plate 303 is prevented, and image scratches (rubbing on the image surface side) are prevented. Generation of scratches is prevented.

  Also in the lower conveyance guide plate 304 in the present embodiment, for example, the rib height 270 (FIG. 12B) of the bent portion of the guide rib 351 is formed lower than the rib height 271 other than the bent portion (FIG. 12B). doing. In the guide ribs (projection ribs) 351 to 358 in the curved guide portion 301b, the protrusion amount of the rib top portion from the outer guide surface 304b is smaller than the protrusion amount of the rib top portion from the guide surface 304a of the flat guide portion 301a. In other words, the guide ribs 351 to 358 in the curved guide portion 301 b of the lower conveyance guide plate 304 have a rib top protrusion amount (rib height 270) that is greater than the rib top protrusion amount in the flat guide portion 301 a of the lower conveyance guide plate 304. It has a wide area portion 351a that is lowered. (See FIGS. 10 (a) and 11 (a))

  In the sheet conveying apparatus 300, as described above, since the sheet is conveyed in a pulling system in order to prevent rubbing scratches on the image surface side, the lower conveying guide having no rib top protrusion amount as described above is set. The following inconveniences that occur in the case of the plate 304 do not occur. That is, when conveying a thick and highly glossy sheet, in the lower conveyance guide plate 200 with no rib top protrusion amount setting shown in FIG. 16B as a comparative example, the sheet S is formed at the bent portion 201a of the guide rib 201. It is rubbed strongly, and the gloss of the rubbed part is lowered. Thereby, the gloss streak is visually recognized over the entire surface of the sheet S in the conveyance direction.

  In order to prevent the occurrence of the inconvenience as described above, in the present embodiment, rib heights 271 other than the wide area portion 351a, such as the wide area portion 351a formed in the bent portion of the guide rib 351 shown in FIGS. The contact area to the sheet S is increased by forming a lower area. Parts other than the wide area part 351a mean the guide ribs 351-358 in the flat guide part 301a, for example. As a result, the contact pressure with the sheet S is reduced to prevent the occurrence of gloss streaks. The function of preventing the sheet S from sticking is maintained by reducing the rib height 270 of the wide area portion 351a without changing the rib height 271 other than the wide area portion 351a of the bent portion.

  Also in the present embodiment, the guide ribs 351 to 358 can be integrally formed with the lower transport guide plate 304, and the integrally formed guide ribs 351 to 358 and the lower transport guide plate 304 can be made of sheet metal.

  According to the present embodiment described above, the guide ribs 351 to 358 extending along the sheet conveyance direction so as to come into contact with the sheet that protrudes from the outer guide surface 304b of the curved guide portion 301b and continues to the flat guide portion 301a. Is formed. Further, the guide ribs 351 to 358 are formed so that the contact area to the sheet at the curved guide portion 301 b is larger than the contact area to the sheet at the flat guide portion 301 a of the lower conveyance guide plate 304. Accordingly, the sheet contact area at the curved guide portion 301b of the lower conveyance guide plate 304 is formed to be larger than the contact area with the sheet at the flat guide portion 301a of the lower conveyance guide plate 304.

  For this reason, the contact pressure between the guide ribs 351 to 358 and the sheet in the curved guide portion 301b of the lower conveyance guide plate 304 can be reduced. In particular, it is possible to suppress gloss streaks and gloss unevenness of an image forming surface due to strong rubbing during double-sided image formation (double-sided printing) or face-down, and to provide a sheet conveying apparatus 300 corresponding to a wide range of sheet types. be able to.

48, fixing section, 60, image forming apparatus (color image forming apparatus), 100, 300, sheet conveying apparatus, 101, 102, 301, 302, ... conveying section (upstream conveying roller, downstream conveying roller), 103, 220 ... Guide members (upper conveyance guide plate, lower conveyance guide plate), 200a, 301a ... Flat guide portion, 200b, 301b ... Curved guide portion, 220a ... Guide surface, 220b ... Guide surface ( outer guide surface ) , 221-228 , 351 to 358... Projecting ribs (guide ribs), 221 a, 351 a... Wide area portion, 230, 270. Plate), 304a ... guide surface, 304b ... guide surface ( outside guide surface ) , 413 ... image forming unit, A ... sheet conveying direction

Claims (7)

In a sheet conveying apparatus provided with a guide member having a flat guide portion and a curved guide portion formed continuously,
The guide member, the protruding ribs extending along the sheet conveying direction, the flat guide portion and protrudes from the guide surface of the curved guide section is formed by Uni continuously by contacting the sheet to be conveyed,
The protruding rib has a shape that gradually spreads from the rib top toward the guide surface, and the length in the width direction orthogonal to the sheet conveying direction of the rib top at the curved guide portion is the flat guide portion. than a length of the width direction of the rib apex is configured to become longer so,
The sheet conveying apparatus , wherein a protruding amount of the rib top portion from the guide surface at the curved guide portion is smaller than a protruding amount of the rib top portion from the guide surface at the flat guide portion . The site amount of projection of the rib top is small, the sheet conveying direction upstream at a predetermined distance toward the downstream is provided with a plurality of sheet conveying apparatus according to claim 1, wherein a. Each of the guide member includes a conveyance unit that conveys the sheet on the upstream side and the downstream side in the sheet conveyance direction,
3. The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is configured such that a conveying speed of the downstream conveying unit is higher than a conveying speed of the upstream conveying unit. The projecting rib, the center in the width direction perpendicular to the sheet conveying direction are arranged so as to spread outwardly toward the sheet conveying direction downstream of any one of claims 1 to 3, characterized in that Sheet conveying device. The projecting rib, the guide member is integrally molded, it sheet conveying device of any one of claims 1 to 4, characterized in. The sheet conveying apparatus according to claim 5, wherein the protruding rib and the guide member are made of sheet metal. An image forming unit for forming an image on a sheet;
A sheet conveying apparatus according to any one of claims 1 to 6 , which conveys an image-formed sheet,
The image forming apparatus according to claim 1, wherein the guide member is disposed downstream of a fixing unit that fixes a toner image formed on the sheet in the image forming unit.

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