JP2019055862A - Sheet conveyance device and image formation device - Google Patents

Abstract

To accurately make a sheet abut onto a registration roller regardless of rigidity of a sheet.SOLUTION: A sheet conveyance device comprises: a pair of conveyance rollers 58 for conveying a sheet; a pair of registration rollers 57 arranged downstream of the pair of conveyance rollers 58; and a guide part for guiding the sheet conveyed by the pair of conveyance rollers 58 and reaching the pair of registration rollers 57, so as to deflect. The guide part so guides the sheet that the number of nodes of the deflection is varied according to rigidity of the sheet.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a sheet conveying apparatus capable of correcting inclination of a conveyed sheet or the like with respect to the conveying direction, so-called skew feeding, and an image forming apparatus such as a copying machine, a facsimile, or a printer including the sheet conveying apparatus.

  A sheet fed from a cassette or the like containing a sheet is fed due to various reasons such as the shape of the conveying roller being tapered or the alignment of the conveying roller being deviated from the image forming unit or transfer unit. , May be skewed during transport.

  In particular, when picking up a sheet from a cassette or separating sheets so that a plurality of sheets are not conveyed simultaneously, the roller width may be narrow or the sheet may not be sufficiently held against turning, The sheet tends to skew.

  Therefore, in order to obtain a good output image, it is necessary to correct the skew of the sheet before the image forming unit transfers the image to the sheet. The correction position is more effective when close to the image forming unit.

  As a means for correcting the skew of the sheet, it is common to correct the skew by abutting the nip portion of the registration roller pair and bending the sheet. However, the abutting force on the roller nip portion due to the bending of the sheet changes due to the difference in stiffness (rigidity) of the sheet. In the case where the pressing force of the sheet against the roller nip is weak, the sheet does not hit the registration roller pair. Conversely, when the abutting force is strong, there is a problem that the sheet penetrates through the nip portion of the registration roller pair.

  In order to solve the above-mentioned problem, Patent Document 1 discloses that the curvature of bending is changed by pushing up different guides depending on the stiffness of the sheet, and the abutting force to the nip portion of the registration roller pair is made appropriate. Has been proposed.

  Also, cited document 2 proposes that it is preferable to make an S-shaped bend as viewed from the cross section of the conveyed sheet in order to make uniform contact with the nip portion of the registration roller pair. Yes.

JP-A-6-191686 JP2003-72982A

  However, when an S-shaped bend is formed on a sheet in a narrow space due to recent downsizing of the apparatus, the curvature of the bend becomes small. Then, when a sheet having high rigidity, for example, a thick sheet, is conveyed so as to form an S-shaped bend having a small curvature, the sheet is deformed into a bend shape. There is concern that the printed image will be disturbed).

  Further, the force with which the deflection is to be extended at the same deflection amount (feed amount of the conveying roller) becomes larger as the number of the bent nodes (the number of curved portions) increases. For example, when the sheet is bent into an S-shape (node number 3), the torque for conveying the sheet in order to make the conveying roller bend is larger than when the sheet is bent into a C-shape (node number 2). Greatly needed. For this reason, there is a concern that the apparatus becomes large, or the skew of the sheet remains due to the leading end of the sheet passing through the nip portion of the registration roller pair.

  SUMMARY An advantage of some aspects of the invention is to provide a sheet conveying apparatus and an image forming apparatus including the sheet conveying apparatus that can accurately strike the sheet against the roller regardless of the rigidity of the sheet.

  A typical configuration according to the present invention includes a first conveyance roller pair that conveys a sheet, a second conveyance roller pair that is disposed downstream of the first conveyance roller pair, and the first conveyance roller pair. And a guide portion that guides the sheet reaching the second pair of conveyance rollers so as to bend, and the guide portion changes the number of the bending nodes according to the rigidity of the sheet. It is characterized by guiding.

  In the present invention, when the sheet is conveyed while forming a bend between the first conveying roller pair and the second conveying roller pair, by changing the bending node according to the rigidity of the sheet, Accurate skew correction can be performed regardless of the stiffness of the sheet.

1 is a cross-sectional view illustrating a schematic configuration of a printer that is an example of an image forming apparatus according to an embodiment of the present invention. The perspective view explaining the structure of the skew feeding correction part in 1st Embodiment. Sectional drawing explaining the structure of the skew correction part in 1st Embodiment. Sectional drawing explaining operation | movement of skew correction of the sheet | seat with low rigidity in the skew correction part in 1st Embodiment. Sectional drawing explaining operation | movement of skew correction of the sheet | seat with high rigidity in the skew correction part in 1st Embodiment. The perspective view explaining the structure of the skew feeding correction part in 2nd Embodiment. Sectional drawing explaining the structure of the skew correction part in 2nd Embodiment. Sectional drawing explaining the operation | movement of skew correction of the sheet | seat with low rigidity in the skew correction part in 2nd Embodiment. Sectional drawing explaining the operation | movement of skew correction of the sheet | seat with high rigidity in the skew correction part in 2nd Embodiment. Sectional drawing explaining the structure of the skew correction part in 3rd Embodiment. Sectional drawing explaining the operation | movement of skew correction of the sheet | seat with low rigidity in the skew correction part in 3rd Embodiment. Sectional drawing explaining the operation | movement of skew correction of the sheet | seat with high rigidity in the skew correction part in 3rd Embodiment.

  Next, the sheet conveying apparatus of the present invention will be specifically described by taking an image forming apparatus using the sheet conveying apparatus as an example.

[First Embodiment]
<Overall configuration of image forming apparatus>
FIG. 1 is an explanatory cross-sectional view of an image forming apparatus 100. An image reading unit that reads an original D placed on a platen glass 120a as an original placing table by an automatic original feeder 120 is provided above an image forming apparatus main body 101. 130 is provided. Below the image reading unit 130, an image forming unit 102, a sheet conveying device 103 that feeds the sheet S to the image forming unit 102, and a manual feeding unit 104 are provided.

  The image forming unit 102 includes a laser scanner unit 111, a photosensitive drum 112, a developing device 113, and the like.

  The sheet conveying device 103 includes a plurality of sheet storages 11 that store the sheets S and are detachable from the image forming apparatus main body 101, a pickup roller 21 that sends out the sheets S stored in the sheet storages 11, and the like. Yes.

  The manual feed unit 104 is provided on the side surface of the image forming apparatus main body 101 which is the apparatus main body so as to be freely opened and closed. The manual feed unit 104 feeds the sheet S stacked on the feeding tray 71 and the feeding tray 71 on which the sheets S are stacked. A roller 51 and the like are provided. When using the manual feed unit 104, the feeding tray 71 is opened and protruded to a position where the sheet can be fed, and the user sets a desired sheet on the protruding feeding tray 71. To feed. In FIG. 1, C is a control unit.

  Next, an image forming operation of the image forming apparatus 100 having such a configuration will be described. When an image reading signal is output to the image reading unit 130 from the control unit C provided in the image forming apparatus main body 101, the image reading unit 130 reads an image. Thereafter, a laser beam corresponding to the electrical signal is emitted from the laser scanner unit 111 onto the photosensitive drum 112.

  At this time, the photosensitive drum 112 is charged in advance, and an electrostatic latent image is formed by irradiation with light. Then, the electrostatic latent image is developed by the developing device 113, whereby toner is formed on the photosensitive drum. An image is formed. The toner image formed in this way is primarily transferred onto the outer periphery of the intermediate transfer belt 110, whereby a toner image is formed on the intermediate transfer belt 110.

  When a feeding signal is output from the control unit C to the sheet conveying device 103, the sheet S is sent out by the pickup roller 21 from the sheet storage 11 that is a sheet storage unit. When a feeding signal is output from the control unit C to the manual feeding unit 104, the sheet S is sent out by the feeding roller 51 from a feeding tray 71 that is a sheet storage unit. Thereafter, the fed sheet S is corrected for skew by a skew correction unit including the registration roller pair 57 and the like, and then synchronized with the toner image on the intermediate transfer belt 110 and the secondary transfer belt 110. The image is sent to a transfer portion constituted by the transfer roller 118.

  The toner image is transferred to the sheet sent to the transfer unit, and then conveyed to the fixing unit 114. By being heated and pressed by the fixing unit 114, the unfixed transfer image is permanently fixed on the sheet S, and the sheet on which the image has been fixed is discharged from the image forming apparatus main body 101 to the discharge tray 117 by the discharge roller 116.

<Sheet conveying device>
Next, a sheet conveyance device that conveys a sheet to the image forming unit 102 will be described focusing on the configuration of a skew correction unit for correcting the skew of the conveyed sheet.

  2 is a perspective view of the skew feeding correction portion, and FIG. 3 is a cross-sectional view of the skew feeding correction portion. A pair of conveying rollers 58 including a driving roller 58a and a driven roller 58b is arranged in the sheet conveying path, and a resist composed of a driving roller 57a and a driven roller 57b is disposed downstream in the sheet conveying direction (hereinafter referred to as “downstream”). A pair of ration rollers 57 is arranged. The fed sheet is conveyed to a registration roller pair 57 which is a second roller pair by a conveyance roller pair 58 which is a first conveyance roller pair, and the leading end of the registration roller pair 57 which is stopped. The sheet skew is corrected by abutting the nip portion with a predetermined pressing force.

  Between the conveying roller pair 58 and the registration roller pair 57, a first fixed guide 63 is provided on one side of the sheet conveying path. The first fixed guide 63 is curved so as to be separated from the nip line Nh of the conveyance roller pair 58 downstream of the conveyance roller pair 58, and thereafter guides the sheet toward the nip portion of the registration roller pair 57. It has become.

  A second fixed guide 64 is disposed on the upstream side (hereinafter “upstream”) of the registration roller pair 57 in the sheet conveyance direction and on the driving roller 58a side, and on the driven roller 58b side of the conveyance roller pair 58 in the third direction. The fixed guide 65 is arranged.

  A movable guide 62 for guiding the sheet sent out by the conveying roller pair 58 is attached to the first fixed guide 63 so as to be rotatable in the direction of arrow A in FIG. The movable guide 62 is disposed in the vicinity of the downstream of the conveying roller pair 58, and is normally urged by an urging member such as a spring (not shown) and is in the state of the solid line in FIG. 3, and is pressed by the conveyed sheet. It can be displaced in the state of the broken line in FIG. 3 against the urging force of the urging member.

  The movable guide 62 is in the first position when it is in the state of the solid line in FIG. 3. At this time, the guide portion 62b (contact portion) that contacts the conveyed sheet and guides the sheet is the nip line Nh. Rather than the third fixed guide 65 side. Further, the movable guide 62 is in the second position when it is in the state of the broken line in FIG. 3, and at this time, the guide portion is located closer to the first fixed guide 63 than the nip line Nh. That is, the movable guide 62 has a predetermined pressing force or more by the sheet conveyed by the conveying roller pair 58 from the first position where the guide portion that contacts the conveyed sheet is located on one side of the nip line Nh. When it is pressed, it can be displaced to a second position located on the other side of the nip line Nh.

  Further, when the movable guide 62 is in the first position, the angle θ formed by the guide surface and the nip line Nh of the conveying roller pair 58 is 45 ° or less. As a result, the sheet conveyed by the conveying roller pair 58 and in contact with the movable guide 62 is smoothly conveyed along the guide surface.

<Sheet transport state>
Next, the conveyance state of the sheet conveyed to the conveyance roller pair 58 and guided by the movable guide 62 and abutted against the registration roller pair 57 is divided into a case where the sheet stiffness (stiffness strength) is low and a case where it is high. I will explain.

(When transporting a sheet with rigidity lower than the specified value)
The skew correction operation when the stiffness of the sheet S is lower than a predetermined value (for example, in the case of thin paper with a basis weight of 64 g / m ² ) will be described with reference to FIG.

  Since the sheet S sent out by the conveying roller pair 58 has low rigidity, it does not overcome the urging force of the urging member of the movable guide 62 even if it contacts the movable guide 62. For this reason, the movable guide 62 is held at the first position, the sheet is guided to the second fixed guide 64 along the movable guide 62, and further, the first fixed along the second fixed guide 64. After being guided to the guide 63, it reaches the registration roller pair 57 stopped along the first fixed guide 63.

  Even after the leading edge of the sheet reaches the registration roller pair 57, the sheet S is sent out by a predetermined length by the conveyance roller pair 58. As a result, the sheet S is bent between the registration roller pair 57 and the conveyance roller pair 58 from the nip portion of the conveyance roller pair 58 toward the third fixed guide 65 as shown in FIG. Of the registration roller pair 57 and further toward the nip portion of the registration roller pair 57. That is, an S-shaped bend having three bend nodes is produced.

  As described above, when the number of bending nodes increases, the force at which the bending is extended at the same bending amount (feed amount of the conveying roller) becomes larger than when the number of nodes is small. The skew is reliably performed by abutting against the registration roller pair 57 uniformly.

(When conveying a sheet with a stiffness higher than the specified value)
Next, the skew feeding correction operation when the stiffness of the sheet S is higher than a predetermined value (for example, in the case of thick paper having a basis weight of 256 g / m ² ) will be described with reference to FIG.

  Since the sheet S sent out from the conveying roller pair 58 has high rigidity, when it comes into contact with and presses against the movable guide 62, it overcomes the urging force of the urging member of the movable guide 62 and moves the movable guide 62 to the second position side. It is guided to the first fixed guide 63 while being pushed down. Thereafter, the pair reaches the registration roller pair 57 stopped along the first fixed guide 63.

  Even after the leading edge of the sheet reaches the registration roller pair 57, the sheet S is fed by a predetermined length by the conveying roller pair 58. At this time, the sheet S is further bent between the registration roller pair 57 and the conveyance roller pair 58 so as to push down the movable guide 62, and the first fixing is performed from the nip portion of the conveyance roller pair 58 as shown in FIG. It bends along the curvature of the movable guide 62 and the first fixed guide 63 that are bent toward the guide 63 and then moved toward the nip portion of the registration roller pair 57. That is, a C-shaped bend having two bend nodes is generated. The sheet S corrects skew by uniformly abutting the front end of the sheet against the registration roller pair 57 by the bending.

  In the case of a sheet having high rigidity, the radius of curvature of the bending produced by the sheet S increases from Rs (FIG. 4) to Rc (FIG. 5). For this reason, the remaining curl does not stick even with a sheet having high rigidity. Further, since the force with which the deflection is extended at the same deflection amount (feed amount of the conveying roller) becomes smaller as the number of nodes is smaller, the C-shape (node number) is smaller than the S-shape (node number 3). In the bending of equation (2), the torque for conveying the sheet is sufficient to produce the bending of the conveying roller. For this reason, it is possible to reduce the size of the driving device, and it is possible to prevent the skew from remaining due to the leading edge of the sheet passing through the nip portion of the registration roller pair 57.

  As described above, the movable guide 62 is operated in accordance with the rigidity of the sheet, and the sheet is guided and conveyed so that a bending node corresponding to the rigidity is generated in the sheet, so that accurate skew correction is performed regardless of the rigidity of the sheet. Can do.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the first embodiment described above, there is one movable guide, but in the present embodiment, there are two movable guides. Note that the basic configuration of the apparatus of this embodiment is the same as that of the above-described embodiment, and thus a duplicate description is omitted. Here, a configuration that is a feature of this embodiment will be described. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

(First movable guide)
6 is a perspective view of the skew feeding correction portion, and FIG. 7 is a cross-sectional view of the skew feeding correction portion. The first fixed guide 63 is provided with a first movable guide 62 that can rotate in the direction of arrow A in FIG. 7 about a rotation shaft 62 a located in the vicinity of the conveying roller pair 58. The first movable guide 62 has a guide portion 62b (contact portion) that contacts the sheet conveyed by the conveying roller pair 58 on one side (the driven roller 58b side) across the nip line Nh of the conveying roller pair 58. ) Is displaceable from a first position (solid line position in FIG. 7) to a second position (dotted line position in FIG. 7) located on the other side (drive roller 58a side) of the nip line Nh. It has become.

  The first movable guide 62 is urged by an urging member such as a spring (not shown) and is normally at the first position. When the first movable guide 62 is pressed by the conveyed sheet, the urging force of the urging member is applied. Accordingly, it can be displaced to the second position.

(Second movable guide)
A fourth fixed guide 60 is provided downstream of the first fixed guide 63 and in the vicinity of the upstream of the registration roller pair 57. The fourth fixed guide 60 is provided with a rotating shaft 61a. A second movable guide 61 that can rotate in the direction of arrow B in FIG. 7 is provided at the center. The second movable guide 61 is a first position (a position indicated by a solid line in FIG. 7) in which a guide surface 61b (contact portion) that comes into contact with the conveyed sheet is positioned in the vicinity of the nip line Nr of the registration roller pair 57. ) To a second position (a position indicated by a broken line in FIG. 7) that moves away from the nip line when the rigidity of the sheet conveyed by the first conveying roller pair is pressed by a sheet having a predetermined value or more. The second movable guide 61 is urged by an urging member such as a spring (not shown) and is normally at the first position. When the second movable guide 61 is pressed by the conveyed sheet, the urging force of the urging member is applied. Accordingly, it can be displaced to the second position.

  Further, a third fixed guide 65 is disposed opposite the first movable guide 62, and a second fixed guide 64 is disposed opposite the second movable guide 61.

(When transporting a sheet with rigidity lower than the specified value)
In the sheet conveying apparatus having the above-described configuration, the skew feeding correction operation when the stiffness of the sheet S is lower than a predetermined value (for example, in the case of thin paper having a basis weight of 64 g / m ² ) will be described with reference to FIG.

  Since the sheet S sent out from the conveying roller pair 58 has low rigidity, it does not overcome the urging force of the urging member of the first movable guide 62 even if it comes into contact with the first movable guide 62. Therefore, the first movable guide 62 is held in the first position, and the sheet is guided to the second fixed guide 64 along the first movable guide 62, and further along the second fixed guide 64. Guided to the second movable guide 61. Even if the sheet comes into contact with the second movable guide 61, the rigidity is low, so the urging force of the urging member of the second movable guide 61 is not overcome, and the second movable guide 61 is in the first position. Retained. After being guided by the second movable guide 61, it reaches the registration roller pair 57 stopped along the fourth fixed guide 60.

  Even after the leading edge of the sheet reaches the registration roller pair 57, the sheet S is sent out by a predetermined length by the conveyance roller pair 58. As a result, the sheet S is bent in an S shape between the registration roller pair 57 and the conveyance roller pair 58 as in the first embodiment described above. That is, as shown in FIG. 8, it bends from the nip portion of the conveying roller pair 58 to the third fixed guide 65 side, then bends to the second movable guide 61 side, and further to the nip portion of the registration roller pair 57. Deflection toward.

  As a result, the sheet S is reliably skewed by the S-shaped bend having three bend nodes and the leading end of the sheet S abutting against the registration roller pair 57 uniformly.

(When conveying a sheet with a stiffness higher than the specified value)
Next, the skew feeding correction operation when the stiffness of the sheet S is higher than a predetermined value (for example, in the case of thick paper having a basis weight of 256 g / m ² ) will be described with reference to FIG.

  The sheet S sent out from the conveyance roller pair 58 is conveyed while pressing the first movable guide 62. At this time, since the rigidity of the sheet is high, the sheet is guided to the second movable guide 61 while overcoming the biasing force of the biasing member of the first movable guide 62 and pushing the movable guide 62 down to the second position side. Similarly to the case of the first movable guide 62, the sheet S has high rigidity with respect to the second movable guide 61, so that the urging force of the urging member of the movable guide 61 is overcome and the movable guide 61 is moved to the first movable guide 61. It reaches the registration roller pair 57 stopped along the movable guide 61 while being pushed down to the position 2 position.

  Even after the leading edge of the sheet reaches the registration roller pair 57, the sheet S is fed by a predetermined length by the conveyance roller pair 58 and is further moved between the registration roller pair 57 and the conveyance roller pair 58. By pushing down the guide 62 and the second movable guide 61, the sheet S is shaped like a C-shaped bend having two bend nodes. With this bending, the sheet S uniformly abuts against the registration roller pair 57 to correct skewing.

  Thereby, the curvature radius Rc of the bending made by the sheet S becomes larger than the curvature radius Rs (see FIG. 8) at the time of the S-shaped bending shown in FIG. 8, so that the sheet is deformed into a bending shape. Even with a highly rigid sheet that is prone to so-called residual curl, the residual curl cannot be applied. In the first embodiment, the number of movable guides is one. In the present embodiment, since the second movable guide 61 is provided downstream of the first movable guide 62, each of the sheets having high rigidity is used. When the movable guide is displaced to the second position, the sheet can be bent with a larger radius of curvature than in the first embodiment.

  Similarly to the case of the first embodiment, since the number of C-shaped bending nodes is smaller than the number of S-shaped bending nodes at the same bending amount (feed amount of the conveying roller), the rigidity of Even if the sheet is high, it is possible to prevent the skew of the sheet from passing through the nip portion of the registration roller pair 57 and leaving the skew without increasing the sheet conveying torque of the conveying roller pair 58.

(Stiffness of registration roller pair)
In the present embodiment, the registration roller pair 57 is configured by a roller formed of an elastic body such as rubber, but the driving roller 57a and the driven roller 57b are configured with different stiffnesses. Specifically, a driven roller (first roller) 57b disposed on one side across the sheet conveyance path is more than a drive roller (second roller) 57a disposed on the other side across the sheet conveyance path. Is also composed of high stiffness. The second movable guide 61 is disposed on the one side, that is, the side where the driven roller 57b is disposed across the sheet conveyance path, and the second fixed guide is opposed to the second movable guide 61. 64 is arranged on the other side, that is, on the side where the driving roller 57a is arranged.

  With the configuration described above, the guide surface of the second fixed guide can be configured so that the front end of the sheet does not directly contact the drive roller 57a, and the second fixed guide 64 drives the sheet with low rigidity. It can be prevented from directly hitting the roller 57a. As a result, no matter how the second movable guide 61 is displaced, the leading edge of the sheet to be conveyed first comes into contact with the driven roller 57b having high rigidity and is guided to the roller nip portion. The drive roller 57a, whose rigidity is lowered to increase it, is protected.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. Since the basic configuration of the present embodiment is the same as that of the above-described embodiment, redundant description is omitted, and the configuration that is a feature of the present embodiment will be described here. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  FIG. 10 is a cross-sectional view of the skew correction unit. The configuration of the skew feeding correction unit of this embodiment will be described with reference to FIG.

  This embodiment also has two movable guides between the conveyance roller pair 58 and the registration roller pair 57, and a first movable guide 62 that can rotate in the direction of arrow A is provided downstream of the conveyance roller pair 58. A second movable guide 61 that can be rotated in the direction of arrow B is provided downstream thereof.

  The first movable guide 62 can be displaced to a first position indicated by a solid line in FIG. 10 and a second position indicated by a broken line in FIG. The first position is such that the tip (contact portion) of the guide portion 62b that comes into contact with the conveyed sheet extends from the surface where the guide surface 61b of the second movable guide 61 extends, so that the nip line Nh of the pair of conveyance rollers 58 is reached. The position on the side of The second position is a position away from the nip line Nh when the stiffness of the sheet conveyed by the conveying roller pair 58 is pressed by a sheet having a predetermined value or more.

The second movable guide 61 has a first position (a position indicated by a solid line in FIG. 10) in which the guide surface 61b (contact portion) that contacts the conveyed sheet is positioned in the vicinity of the nip line Nr of the registration roller pair 57. Thus, the sheet can be displaced to a second position (a position indicated by a broken line in FIG. 10) that moves away from the nip line Nr when the rigidity of the sheet conveyed by the conveying roller pair 58 is pressed by a predetermined sheet or more. Each movable guide is urged by an urging member (not shown) and is normally held at the first position. In the present embodiment, as shown in FIG. 10, the first movable guide 62 is used. A flexible guide 66 is provided at a position facing the guide portion when the sheet is at the first position across the sheet conveyance path. The flexible guide 66 is composed of a flexible sheet, and guides the sheet while elastically pushing it back when the loop formed by bending is pressed against the grown sheet.

(When transporting a sheet with rigidity lower than the specified value)
In the sheet conveying apparatus having the above configuration, a skew correction operation when the stiffness of the sheet S is lower than a predetermined value (for example, in the case of thin paper having a basis weight of 64 g / m ² ) will be described with reference to FIG.

  The first movable guide 62 is fed from the conveying roller pair 58 because the rotation tip (guide portion) is located between the nip line Nh of the conveying roller pair 58 and the nip line Nr of the registration roller pair 57. The leading edge of the sheet S reaches the second movable guide 61 without coming into contact with the first movable guide 62. Although the sheet S is guided and conveyed by the second movable guide 61, since the rigidity is low, the urging force of the urging member of the second movable guide 61 is not overcome. For this reason, the sheet S reaches the registration roller pair 57 stopped along the guide surface of the second movable guide 61 held at the first position.

  In the present embodiment, the guide surface 61 b of the second movable guide is disposed so as to have a positional relationship that intersects the nip line Nh of the transport roller pair 58. Thereby, when the leading edge of the sheet conveyed by the conveying roller pair 58 is conveyed without being guided by the first movable guide, it reaches the guide surface 61b of the second movable guide.

  Even after the leading edge of the sheet reaches the registration roller pair 57, the sheet S is fed by a predetermined length by the conveying roller pair 58 until the deflection comes into contact with the first movable guide 62. When the deflection further grows, the rigidity of the sheet S is low, so that the urging force of the urging member of the first movable guide 62 cannot be overcome, and the first movable guide 62 remains held at the first position. It becomes. Then, the sheet S is pushed back by the first movable guide 62 and the upstream deflection grows on the side opposite to the first movable guide 62.

  The deflection of the sheet S grown on the side opposite to the first movable guide 62 abuts on the flexible guide 66 and grows while elastically deforming the flexible guide 66, and finally the registration roller pair 57 and the conveying roller. As shown in FIG. 11, an S-shaped bend occurs between the pair 58.

  As the sheet S bends into an S-shape with three bending nodes, the leading edge of the sheet is uniformly abutted against the registration roller pair 57 to correct skewing.

(When conveying a sheet with a stiffness higher than the specified value)
Next, the skew feeding correction operation when the stiffness of the sheet S is higher than a predetermined value (for example, in the case of thick paper having a basis weight of 256 g / m ² ) will be described with reference to FIG.

  The leading edge of the sheet S sent out from the conveying roller pair 58 reaches the second movable guide 61. Since the rigidity of the sheet S is high, the sheet S stops along the second movable guide 61 while overcoming the biasing force of the biasing member of the second movable guide 61 and pushing the second movable guide 61 toward the retracted position. The registration roller pair 57 is reached. Even after the leading edge of the sheet reaches the registration roller pair 57, when the sheet S is fed by a predetermined length by the conveying roller pair 58, the first movable guide 62 and the second movable sheet 62 are moved because the sheet S has high rigidity. Overcoming the urging force of the urging member of the guide 61, the first movable guide 62 and the second movable guide 61 are further pushed down between the registration roller pair 57 and the conveying roller pair 58, and the sheet S has a C-shape. Form a deflection. The sheet S corrects skew by uniformly abutting the leading end of the sheet against the registration roller pair 57 by C-shaped bending.

  As a result, the radius of curvature of the deflection produced by the sheet S increases from Rs (FIG. 11) to Rc (FIG. 12), so even a highly rigid sheet that is prone to a so-called residual curl that causes the sheet S to be deformed. The remaining curls will not stick.

  Similarly to the above-described embodiment, since the number of C-shaped bending nodes is smaller than the number of S-shaped bending nodes at the same bending amount (feed amount of the conveying roller), the rigidity of Even if the sheet is high, it is possible to prevent the skew of the sheet from passing through the nip portion of the registration roller pair 57 and leaving the skew without increasing the sheet conveying torque of the conveying roller pair 58.

Nh ... nip line Nr ... nip line S ... sheet 57 ... registration roller pair 57a ... drive roller 57b ... driven roller 58 ... transport roller pair 58a ... drive roller 58b ... driven roller 60 ... fourth fixed guide 61 ... second Movable guide 61a ... Rotating shaft 61b ... Guide surface 62 ... First movable guide 62a ... Rotating shaft 63 ... First fixed guide 64 ... Second fixed guide 65 ... Third fixed guide 66 ... Flexible guide 71 ... Feed tray 102 ... Image forming unit 103 ... Sheet conveying device 112 ... Photoconductor drum 116 ... Discharge roller 117 ... Discharge tray

Claims (10)

A first conveying roller pair for conveying a sheet;
A second conveying roller pair disposed downstream of the first conveying roller pair;
A guide portion that guides the sheet that is conveyed by the first conveyance roller pair and reaches the second conveyance roller pair to bend;
Have
The sheet conveying apparatus, wherein the guide unit guides the sheet so as to change the number of the bending nodes according to the rigidity of the sheet.   The sheet conveying apparatus according to claim 1, wherein the guide unit includes a movable guide that is displaced when the stiffness of the sheet conveyed by the first conveying roller pair is pressed by a sheet having a predetermined value or more.   The movable guide is conveyed by the first conveying roller pair from a first position where an abutting portion that contacts the conveyed sheet is located on one side of the nip line of the first conveying roller pair. 3. The sheet conveying apparatus according to claim 2, wherein the sheet conveying apparatus is displaceable to a second position located on the other side of the nip line when the sheet is pressed by a sheet having a predetermined rigidity or more.   The guide portion is disposed downstream of the first movable guide and the first movable guide that are displaced when the stiffness of the sheet conveyed by the first conveyance roller pair is pressed by a sheet having a predetermined value or more. The sheet conveying apparatus according to claim 1, further comprising a second movable guide.   The first movable guide is configured so that the contact portion that contacts the sheet to be conveyed is from a first position where one of the first movable guides is located on one side of the nip line of the first conveyance roller pair. The sheet conveying apparatus according to claim 4, wherein the sheet conveying apparatus is displaceable to a second position located on the other side of the nip line when the rigidity of the sheet conveyed by the sheet is pressed by a sheet having a predetermined value or more.   In the first movable guide, an abutting portion that contacts the conveyed sheet is positioned closer to the nip line of the first conveying roller pair than a surface extending from the guide surface of the second movable guide. Displaceable from the first position to a second position away from the nip line when the stiffness of the sheet conveyed by the first conveying roller pair is pressed by a sheet having a predetermined value or more. The sheet conveying apparatus according to claim 4.   The second movable guide is conveyed by the first conveying roller pair from a first position where an abutting portion that contacts the conveyed sheet is located near the nip line of the second conveying roller pair. 7. The sheet conveying apparatus according to claim 5, wherein the sheet conveying apparatus is displaceable to a second position away from the nip line when the sheet is pressed by a sheet having a predetermined rigidity or higher.   8. The sheet conveying apparatus according to claim 6, wherein a guide surface of the second movable guide intersects a nip line of the first conveying roller pair. 9. The second conveying roller pair includes a first roller disposed on one side across the sheet conveying path and a second roller having higher rigidity than the first roller disposed on the other side. And
5. The second movable guide is disposed on the other side across the sheet conveyance path, and a fixed guide is disposed on the one side facing the second movable guide. The sheet conveying apparatus according to claim 8. In an image forming apparatus for forming an image on a sheet,
A sheet conveying device according to any one of claims 1 to 9,
An image forming unit that forms an image on the sheet conveyed by the sheet conveying device;
An image forming apparatus comprising:

Images