JP2011136809A - Sheet conveying device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet conveying device which can achieve high integrity and accuracy, with respect to a variety of sheets, without causing damages such as a buckling and a folding to the sheets, and to provide an image forming apparatus. <P>SOLUTION: According to the image forming apparatus 18, a control unit 15 selects a thin sheet P so as to send it to a bend-shaped conveying passage 40, and a flapper 23 can be switched so as to convey the sheet P to the selected bend-shaped conveying passage 40. As a result, the damages such as the buckling and the folding of a sheet side end when the thin sheet is conveyed can be prevented, the damages being typical when using a skew conveying roller and the like, and the sheet conveying device 20 which can achieve high integrity and accuracy can be provided without causing damages to the sheet. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sheet conveying apparatus that controls the posture and position of a sheet to be conveyed, and an image forming apparatus such as a copying machine and a printer including the sheet conveying apparatus.

  In an image forming apparatus such as a copying machine or a printer that applies electrophotographic technology, after a toner image formed on an image carrier such as a photosensitive drum is transferred to a sheet in an image forming unit, a heat fixing device or a pressure fixing device An image is obtained by fixing a toner image on a sheet by a fixing device such as the above. In such an image forming apparatus, a sheet conveying unit that conveys a sheet along a conveying path provided in an image forming unit, a fixing device, or the like is provided. Further, a sheet aligning device that corrects the posture and position of the sheet being conveyed is disposed upstream of the image forming unit in the conveyance path, and prevents a deviation between the sheet conveyed to the image forming unit and the transferred image. I am doing so.

  Conventionally, as one form of the sheet aligning device, the sheet side edge is obtained by narrowing the sheet with a skew feeding roller with respect to a reference surface along the sheet conveyance direction and conveying the sheet side edge against the reference surface. There is a technique for performing sheet alignment based on a side (see Patent Document 1).

  FIG. 9 shows an example of a sheet aligning device using skew feeding rollers. The sheet aligning apparatus shown in FIG. 9 includes skew feeding rollers 101, 102, and 103 and a side guide 104, and transports the conveyed sheet P in the direction of the feeding force of the skew feeding rollers 101 to 103 (the direction of arrow 110). To do. Thereafter, the side edge E of the sheet P is conveyed in the sheet conveyance direction (arrow 111 direction) while abutting on the reference surface 104a of the side guide 104, thereby correcting the posture of the sheet P with the side edge E as a reference. Here, the conveying force and the inclination angle of the skew feeding rollers 101 to 103 are set so that the side edge E of the sheet P is in contact with the reference surface 104a of the side guide 104 so as to obtain high alignment accuracy. Yes.

Japanese Patent Publication No. 2-59096

  However, in the sheet aligning apparatus shown in FIG. 9, when a sheet having low rigidity (rigidity) such as thin paper is conveyed, the side of the sheet on which the force pressed against the reference surface 104a of the side guide 104 continues to act during conveyance. There was a problem that buckling or bending occurred at the edge (side edge).

  On the other hand, when a highly rigid sheet such as thick paper is conveyed, the resistance of the sheet to the conveyance guide that guides the sheet along the conveyance path where the oblique feeding roller is arranged increases due to the curl of the sheet. The contact state of the side guide with the reference surface becomes unstable. As a result, there is a problem that sufficient alignment accuracy cannot be obtained.

  SUMMARY OF THE INVENTION Accordingly, the present invention provides a sheet conveying apparatus capable of obtaining high alignment accuracy without causing damage such as buckling and bending to a wide variety of sheets, and an image forming apparatus including the sheet conveying apparatus. With the goal.

  The present invention provides a sheet conveyance device including a skew correction unit that corrects skew of a sheet being conveyed, wherein the skew correction unit includes a plurality of conveyance paths having different curvatures and a plurality of conveyance paths. The sheet is conveyed by each conveyance path, and is adjusted by a width-adjusting roller so that the skew is corrected while the side edge of the sheet is in sliding contact with a reference surface arranged along the sheet conveying direction. A sheet correction mechanism, a control unit that selects a conveyance path so that the sheet is fed along a conveyance path with a larger curvature as the basis weight of the sheet whose skew is corrected is smaller, and a sheet that passes through the conveyance path selected by the control unit. And a switching unit that switches the sheet conveyance direction so as to be conveyed.

  The present invention is also directed to a sheet conveying apparatus including a skew correction unit that corrects skew of a conveyed sheet, wherein the skew correction unit includes a plurality of conveyance paths having different bending directions, and the plurality of conveyances. Provided in each of the paths, the sheets conveyed in the respective conveying paths are aligned by the width-adjusting roller, and the sheet is skewed while the side edges of the sheet are in sliding contact with the reference surface arranged along the sheet conveying direction. A skew correction mechanism for correcting, and a curl detection unit that is disposed upstream of the conveyance path in the sheet conveyance direction and detects the curl state of the sheet whose skew is corrected, and is detected by the curl detection unit. A control unit that selects a conveyance path having a curvature in the same direction as the curl direction of the sheet, and a switching unit that switches the conveyance direction of the sheet so that the sheet is conveyed to the conveyance path selected by the control unit, Characterized by comprising It is.

  According to the present invention, the control unit selects a conveyance path having a larger curvature as the basis weight of the sheet is smaller, and the switching unit switches so that the sheet is conveyed on the conveyance path selected by the control unit. A more reliable sheet alignment operation can be performed for various sheets. Accordingly, it is possible to provide a sheet conveying apparatus that can obtain high alignment accuracy without damaging the sheet.

  According to the present invention, the control unit selects a curved conveyance path in the same direction as the curl of the sheet, and the switching unit switches the conveyance direction so that the sheet is conveyed to the conveyance path selected by the control unit. Thus, it is possible to perform a more reliable sheet alignment operation for a wide variety of sheets. Accordingly, it is possible to provide a sheet conveying apparatus that can obtain high alignment accuracy without damaging the sheet.

1 is a schematic diagram illustrating an image forming apparatus including a sheet conveying device according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view of the sheet conveying apparatus according to the first embodiment. 1 is a schematic diagram of a sheet conveying apparatus according to a first embodiment. Explanatory drawing of the operation | movement matched while correcting the skew of the sheet | seat in 1st Embodiment. FIG. 10 is a schematic diagram illustrating an image forming apparatus including a sheet conveying device according to a second embodiment of the present invention. FIG. 10 is a perspective view schematically illustrating a sheet conveying device according to a second embodiment. Explanatory drawing which shows operation | movement of the sheet conveying apparatus in 2nd Embodiment. 9 is a flowchart for explaining selection of a conveyance path in the second embodiment. Explanatory drawing of the operation | movement matched while correcting the skew of a sheet | seat in a prior art example.

<First Embodiment>
The first embodiment according to the present invention will be described below. FIG. 1 is a schematic diagram of an image forming apparatus including a sheet conveying device 20 according to the present embodiment. The image forming apparatus 18 is a digital full color printer that forms a full color image.

  The image forming apparatus 18 shown in FIG. 1 includes image forming units 1Y, 1M, 1C, and 1K that perform from laser exposure to toner image formation for each color of yellow, magenta, cyan, and black. Further, the image forming apparatus 18 primarily transfers the toner images of the respective colors formed in the image forming unit on the intermediate transfer belt 2 moving in the direction of the arrow 10 and then transfers the toner images to the sheet at the secondary transfer point A. An image transfer device 3 for next transfer is provided.

  Further, the image forming apparatus 18 includes sheet cassettes C1 and C2, sheet feeding units 11 and 12 that feed sheets from the sheet cassettes C1 and C2, a sheet feeding and conveying unit 13, and a control unit 15. The control unit 15 comprehensively controls the entire apparatus, and sends the sheet P through a conveyance path (curved conveyance path 40 in the present embodiment) having a larger curvature as the basis weight of the sheet P whose skew is corrected is smaller. Select the transport path.

  The image forming apparatus 18 controls the posture and position of the sheet, and also includes a sheet conveying device 20 that conveys the sheet to the secondary transfer point A in accordance with the timing of the toner image on the intermediate transfer belt 2, and the fixing device 5. I have. Further, the image forming apparatus 18 includes a fixing conveyance unit 6 that conveys the sheet on which the toner image is secondarily transferred to the fixing device 5. Further, the image forming apparatus 18 includes a reversing device 7 that reverses the front and back of the sheet when performing double-sided image formation, and a double-sided conveyance unit 8 that conveys the sheet to the sheet feeding conveyance unit 13 again, and a sheet after fixing. And a paper discharge unit 9 for switching the path to the double-sided conveyance unit 8.

  The image forming apparatus 18 according to the present exemplary embodiment includes a sheet conveying device 20 and an image forming unit that forms an image on a sheet conveyed by the sheet conveying device 20. The image forming unit includes an intermediate transfer belt 2 on which a toner image of each color is primarily transferred, a secondary transfer device provided at a secondary transfer point A, and the like.

  Here, the sheet conveying apparatus 20 will be described in more detail. 2A, 2B, 2C and 3A are schematic views of the sheet conveying device 20. FIG. The sheet conveying apparatus 20 includes a linear conveying path 30 including a pair of inclined feeding rollers 31, 32, 33, a curved curved conveying path 40 including a pair of inclined feeding rollers 41, 42, and 43, and the conveying path 30. , 40 and a flapper 23 that can be rotated so as to be switched. The skew feeding roller pairs 31 to 33 and the skew feeding roller pairs 41 to 43 constitute width adjusting rollers, respectively. In the sheet conveying apparatus 20, the sheet P conveyed from the sheet conveying apparatus 13 passes through the conveying roller pair 21 positioned at the uppermost stream part of the sheet conveying apparatus 20, and then the linear conveying path 30 or curved by the flapper 23. It is guided to one of the transport paths 40.

  In the present embodiment, a linear conveyance path having a curvature (reciprocal of the radius of curvature) of 0 is given as an example of the linear conveyance path 30, but the present invention is not limited to this, and has a slight curvature and is slightly curved. Needless to say, such a conveyance path can also be used as the linear conveyance path 30.

  The flapper 23 is rotatably supported by a shaft 27, and can be rotated and stopped at a desired timing by a driving device (not shown). The flapper 23 and a driving device (not shown) constitute a switching unit that switches the conveyance direction of the sheet P so that the sheet P is conveyed on the conveyance path selected by the control unit 15. The flapper 23 constitutes a switching lever included in the switching unit.

  The linear conveyance path 30 includes conveyance guides 35a and 35b for guiding the sheet P along the linear conveyance path, and three sets of skew feeding roller pairs 31, 32, and 33 arranged along the linear conveyance path. And. The curved conveyance path 40 includes conveyance guides 45a and 45b for guiding the sheet P along the curved conveyance path, and three sets of skew feeding roller pairs 41, 42, and 43 arranged along the curved conveyance path. I have.

  The sheet P that has passed through one of the linear conveyance path 30 and the curved conveyance path 40 having different curvatures is conveyed along a conveyance path that merges before the registration roller pair 22, and is subjected to secondary transfer by the registration roller pair 22. Sent to point A (see FIG. 1). Further, on the downstream side of the registration roller pair 22, conveyance guides 26a and 26b for guiding the sheet P to the secondary transfer point A and a sheet timing sensor S2 for detecting the passage timing of the leading edge of the sheet P are arranged. Yes.

  The conveying roller pair 21, the registration roller pair 22, and the skew feeding roller pairs 31 to 33 and 41 to 43 are driven by a driving device (not shown) to convey the sheet P. The pair of skew feeding rollers 31 to 33 is provided with a roller separation device (not shown) so that the upper rollers 31a, 32a and 33a can be brought into contact with and separated from the lower rollers 31b, 32b and 33b at a desired timing. ing. Each of the skew feeding roller pairs 41 to 43 is provided with a roller separating device (not shown) so that the upper rollers 41a, 42a and 43a can be brought into contact with and separated from the lower rollers 41b, 42b and 43b at a desired timing. It is configured.

  In this embodiment, the linear conveyance path 30, the curved conveyance path 40, the skew correction mechanism, the control unit 15, and the flapper 23 constitute a skew correction unit that corrects the skew of the conveyed sheet P. Yes. The skew feeding correction mechanism is provided in each of the transport paths 30 and 40, and the sheets P transported in the transport paths 30 and 40, respectively, are made closer to each other by the skew feeding roller pairs 31 to 33 and 41 to 43, and a reference is made. The skew is corrected while the side edge E of the sheet P is in sliding contact with the surface 25a.

Next, the sheet alignment operation by the sheet conveying device 20 will be described. That is, when the sheet P passes through the sheet conveying apparatus 20, the conveying path is selected based on the sheet information registered for the sheets P stored in the sheet cassettes C1 and C2. In the present embodiment, the sheet type is classified into thin paper, plain paper, and thick paper according to the basis weight, and the conveyance path is switched according to the sheet type. Normally, sheets used in image forming apparatuses such as copying machines and printers have a basis weight of 64 to 105 g / m ² (predetermined value) with plain paper and a basis weight of a predetermined value (basis weight of plain paper). Generally, small paper is classified as thin paper, and paper having a basis weight larger than a predetermined value is classified as thick paper. For this reason, also in this embodiment, sheets are classified based on the same definition.

  When the sheet P conveyed from the sheet conveying unit 13 to the sheet conveying apparatus 20 is plain paper or thick paper, the flapper 23 that is waiting or rotated at the position indicated by reference numeral 23a in FIG. The sheet P conveyed from the roller pair 21 is guided to the linear conveyance path 30.

  Next, as illustrated in FIG. 3B, the sheet P is laterally moved in the direction of the side guide 25 by the skew feeding roller pairs 31 to 33, and then the side end toward the reference surface 25 a disposed along the sheet conveyance direction. It is conveyed in the conveying direction (arrow 28 direction) with E in contact (sliding contact). Then, with the side guide 25 as a reference, positioning and posture correction in a direction (width direction) orthogonal to the sheet conveyance direction (arrow 28 direction) are performed. Thereafter, the sheet P is guided to the registration roller pair 22, and when the sheet timing sensor S2 detects the passage of the leading edge of the sheet P, the upper rollers 31a to 33a of each of the skew feeding roller pairs 31 to 33 are not shown. Thus, they are separated in the direction of arrow C shown in FIG. Thereby, the sheet alignment operation by the sheet skew correction in the linear conveyance path 30 is completed.

  Further, the registration roller pair 22 is controlled as follows based on the passage timing of the leading edge of the sheet P detected by the sheet timing sensor S2. That is, the registration roller pair 22 moves the sheet P to the secondary transfer point A in accordance with the toner image passage timing on the intermediate transfer belt 2 detected by the image timing sensor S1 (see FIG. 1) provided in the image transfer device 3. Transport to. Thereby, the sheet alignment operation as the sheet conveying apparatus 20 is completed.

  On the other hand, when the sheet P conveyed from the sheet feeding / conveying unit 13 to the sheet conveying apparatus 20 is thin paper, the flapper 23 rotates or waits at a position 23b as shown in FIG. Then, the sheet P conveyed from the conveyance roller pair 21 is guided to the curved conveyance path 40. In this curved conveyance path 40, the sheet P is positioned and corrected with respect to the side guide 25 by each of the skew feeding roller pairs 41 to 43, similarly to the operation in the linear conveyance path 30 described above. Thereafter, the sheet is conveyed to the secondary transfer point A by the registration roller pair 22.

  In the curved conveyance path 40, the sheet P conveyed by each of the skew feeding roller pairs 41 to 43 has a side end E curved along the curved conveyance path, as shown in FIG. Abuts (slidably contacts) the reference surface 25a. At this time, the stiffness of the sheet P in the contact direction increases due to the curvature of the side end E.

  In this embodiment, a pair of skew feeding rollers is used as the sheet width-conveying device. However, the sheet is conveyed in the direction of the side guide 25 and conveyed in the conveying direction 28 while abutting the side edge E against the reference surface 25a. As long as it can be performed, other width-shifting conveyance devices may be used.

  As described above, in the sheet conveying apparatus 20 provided in the image forming apparatus 18, the thin paper having low rigidity is selectively guided to the curved conveying path 40 and the alignment operation is performed by each of the skew feeding roller pairs 41 to 43. Therefore, it is possible to prevent a problem that buckling or bending occurs at the side edge E of the sheet P.

  In the present embodiment, the conveyance path of the sheet conveyance device 20 is selected according to the sheet type classified by the sheet basis weight, but the sheet classification based on factors affecting other alignment operations such as sheet stiffness and size, or a plurality of sheets The conveyance path may be selected based on the combination of the sheet characteristics. Then, if the sheet that is likely to buckle or bend at the side edge (side edge) by the alignment operation by the oblique feeding roller is selectively guided to the curved conveyance path 40, the same as in the present embodiment. Further, buckling and bending of the side edge portion of the seat can be prevented.

  In this embodiment, the conveyance path (conveyance path) is selected based on the sheet information registered for the sheets stored in the sheet cassettes C1 and C2. However, the sheet information is input every time the image is formed. It may be. Further, a sheet stiffness measuring device for measuring the stiffness (rigidity) of the sheet being conveyed is provided in the sheet feeding / conveying unit 13 or the like, and the conveyance path (conveyance) of the sheet conveying device 20 according to the sheet stiffness measured by the sheet stiffness measuring device. Road) may be selected.

  Furthermore, in this embodiment, the sheet conveying apparatus 20 is provided with two conveying paths. However, if more conveying paths are provided and the conveying path is selected based on the sheet characteristics, the sheet alignment accuracy can be improved. Further improvement is also possible.

  In the present embodiment described above, the curved conveyance path 40 that is a conveyance path having a larger curvature is selected by the control unit 15 as the basis weight of the sheet P is smaller, and the control unit 15 is selected by the flapper 23 that is a switching lever. It is possible to switch so that the sheet P is conveyed on the curved conveyance path 40. As a result, it is possible to prevent damage such as buckling or folding of the sheet side edge during thin paper conveyance, which is peculiar to the case of using a skew feeding roller, etc., and more reliable sheet alignment operation for a wide variety of sheets. It can be carried out. Therefore, it is possible to realize the sheet conveying device 20 that can obtain high alignment accuracy without damaging the sheet.

  Further, in this embodiment, the linear conveyance path 30 and the curved conveyance path 40 are arranged side by side so as to branch from the paper feed conveyance section 13 that is the upstream main conveyance path, and the switching section is configured as a control section. 15 is provided with a flapper 23 for feeding the sheet P to the curved conveyance path 40 selected at 15. Further, the control unit 15 guides the sheet P having a basis weight of a predetermined value or more to the linear conveyance path 30 having a small curvature, and guides the sheet P having a basis weight less than the predetermined value to the curved conveyance path 40 having a large curvature. The flapper 23 is switched as described above. As a result, a wide variety of sheets can be quickly sent to the conveyance path selected according to the inherent properties.

<Second Embodiment>
FIG. 5 is a schematic view of the image forming apparatus 18 including the sheet conveying device 50 according to the second embodiment of the present invention. The image forming apparatus 18 of this embodiment is a digital full-color printer that forms a full-color image, like the image forming apparatus 18 of the first embodiment. In addition, description of the apparatus configuration and operation that are the same as those in the first embodiment is omitted here.

  In the double-sided conveyance unit 8 of the image forming apparatus 18 in the present embodiment, a sheet curl measurement unit 70 that measures a sheet curl generated when the sheet P passes through the fixing device 5 is disposed. In the image formation on both sides of the sheet P, the sheet curl measuring unit 70 can measure the curl state of the sheet when the sheet P passes through the duplex conveying unit 8. The sheet curl measuring unit 70 is disposed upstream of the first and second curved transport paths 40 and 60, which are transport paths, in the sheet transport direction, and detects the curl state of the sheet P whose skew is corrected. A curl detection unit is configured. In the present embodiment, when a sheet passes through the sheet conveying apparatus 50 during image formation on both sides, in addition to the switching of the conveying path based on the sheet information registered for the sheets stored in the sheet cassettes C1 and C2. Then, the conveyance path is switched based on the sheet curl amount.

  Here, an outline of the sheet conveying apparatus 50 provided in the image forming apparatus 18 will be described. FIG. 5 is a schematic view of the sheet conveying apparatus 50, and FIG. 6 is a perspective view schematically showing the sheet conveying apparatus 50.

  As shown in FIGS. 5 and 6, the sheet conveying apparatus 50 is in a direction (downward) different from the linear conveying path 30, the first curved conveying path 40, and the first curved conveying path 40. And a curved second curved conveyance path 60. The first curved conveyance path 40 and the second curved conveyance path 60 are branched from the sheet feeding conveyance section 13 which is the upstream main conveyance path, and are arranged in parallel up and down. Also in this embodiment, the definition regarding the curvature of the linear conveyance path 30 is the same as that in the first embodiment.

  The straight conveyance path 30 and the first curved conveyance path 40 are respectively provided with skew feeding roller pairs 31 to 33 and 41 to 43 as in the first embodiment. The second curved conveyance path 60 includes a pair of skew feeding rollers 61, 62, and 63 as width adjusting rollers. Each of the skew feeding roller pairs 61 to 63 is provided with a roller separation device (not shown) so that the upper rollers 61a, 62a and 63a can be brought into contact with and separated from the lower rollers 61b, 62b and 63b at a desired timing. Has been.

  In this embodiment, as a conveyance path (conveyance path) switching unit, a flapper 51 is provided in addition to the flapper 23 disposed on the downstream side of the conveyance roller pair 21 as shown in FIG. The sheet P transported from the paper feed transport unit 13 passes through the transport roller pair 21 and is then guided to one of the three transport paths by the flappers 23 and 51.

  In the present embodiment, the sheet is conveyed by the linear conveyance path 30, the first curved conveyance path 40 and the second curved conveyance path 60 having different bending directions, the skew correction mechanism, and the sheet curl measurement unit 70. A skew correction unit for correcting the skew of the coming sheet P is configured. The skew feeding correction mechanism is provided in each of the transport paths 40 and 60. The sheet P transported in the transport paths 40 and 60 is shifted by the skew feeding roller pairs 41 to 43 and 61 to 63, and the reference is made. The skew is corrected while the side edge E of the sheet P is in sliding contact with the surface 25a (see FIG. 3). The control unit 15 in the present embodiment can further select a conveyance path having a curvature in the same direction as the curl direction of the sheet P detected by the sheet curl measurement unit 70 as the curl detection unit. Then, the control unit 15 switches the flappers 23 and 51 so as to guide the sheet P to the selected conveyance path.

  7A, 7 </ b> B, and 7 </ b> C are schematic views of the switching operation of the flapper 23 and the flapper 51 to each conveyance path. The flapper 23 and the flapper 51 are rotatably supported by a shaft 27 and a shaft 52, respectively, and can be rotated and stopped at a desired timing by a driving device (not shown). Perform the action. The flappers 23 and 51 and a driving device (not shown) constitute a switching unit that switches the conveyance direction of the sheet P so that the sheet P is conveyed to the conveyance path selected by the control unit 15 (FIG. 5). The flappers 23 and 51 are included in the switching unit and constitute a switching lever for feeding the sheet P to the conveyance path selected by the control unit 15 of the branched conveyance path. The positions of the flappers 23 and 51 shown in FIGS. 7A to 7C and the conveyance path through which the sheet P is guided are the linear conveyance path 30 in FIG. 7A and the conveyance path in FIG. 7B. The first curved conveyance path 40, which is the second curved conveyance path 60 in FIG.

  In this embodiment, in addition to the switching of the conveyance path according to the sheet type classified according to the sheet basis weight described above, the sheet curl measuring unit 70 is formed after the image formation on the second side when the image is formed on both sides of the thick paper. The conveyance path is switched based on the sheet curl direction measured in (1).

  FIG. 8 is a flowchart for selecting a conveyance path of the sheet conveyance apparatus 50 according to this embodiment. As shown in FIG. 8, in the image forming apparatus 18, when the sheet type is thick paper, the curling of the sheet P is performed when the image is formed on the second surface of the sheet P in the image forming mode for both surfaces of the sheet P. A curved conveyance path that is curved in the same direction as the direction is selected to guide the sheet P.

  That is, when the process starts, the control unit 15 determines the sheet type based on the sheet information (step S1). As a result, when it is determined that the sheet type is plain paper, the flappers 23 and 51 are switched up and down as shown in FIG. 7A to guide the sheet P to the linear conveyance path 30. If it is determined that the sheet type is thin paper, the flappers 23 and 51 are both switched downward as shown in FIG. 7B to guide the sheet P to the first curved conveyance path 40 (S5). .

  If it is determined in step S1 that the paper is cardboard, it is determined in step S2 whether the image forming mode is single-sided or double-sided. If it is determined that the image forming mode is single-sided, the flappers 23 and 51 are displayed as shown in FIG. Switching is performed as in a), and the sheet P is guided to the linear conveyance path 30 (S7). On the other hand, if it is determined in step S2 that both sides are present, it is further determined in step S3 whether the image forming surface is the first surface or the second surface. As a result, when it is determined that it is the first surface, the flappers 23 and 51 are switched as shown in FIG. 7A, and the sheet P is guided to the linear conveyance path 30 (S7).

  Further, when it is determined in step S3 that the second surface is present, the curl direction is determined in step S4 based on the result measured by the sheet curl measurement unit 70. As a result, if it is determined that there is no curl, the flappers 23 and 51 are switched as shown in FIG. 7A, and the sheet P is guided to the linear conveyance path 30 (S7). On the other hand, if it is determined in step S4 that the curl is an upper curl, the flappers 23 and 51 are switched as shown in FIG. 7B, and the sheet P is bent in the same direction as the sheet curl. Guide to the transport path 40 (S5). If it is determined in step S4 that the curl is a lower curl, both flappers 23 and 51 are switched upward as shown in FIG. 7C, and the sheet P is bent in the same direction as the sheet curl. The second curved conveyance path 60 is guided (S6).

  As described above, the sheet conveying apparatus 50 provided in the image forming apparatus 18 guides the sheet P conveyed from the sheet feeding / conveying unit 13 to the conveyance path selected according to the sheet type. In addition to performing P matching, the following processing can be performed. That is, when forming a double-sided image on the sheet P, which is a thick paper having a high rigidity, after the image is formed on the second surface where the sheet curl is likely to occur by passing through the fixing device 5, it is curved in the same direction as the sheet curl. The sheet alignment can be performed by guiding the sheet P to the conveyed path. For this reason, the increase in resistance between the sheet P and the conveyance guide can prevent the problem that the contact (sliding contact) of the sheet P with the side guide 25 becomes unstable and sufficient alignment accuracy cannot be obtained. .

  As described above, in this embodiment as well, damage caused by buckling or bending of the sheet side edge during thin paper conveyance, and misalignment due to curling during thick paper conveyance, which is peculiar to the case of using a skew feeding roller or the like, are prevented. be able to. As a result, a more reliable sheet alignment operation can be performed on a wide variety of sheets, and the sheet conveying apparatus 50 that can obtain high alignment accuracy without damaging the sheet can be realized.

  In this embodiment, the sheet curl measurement unit 70 that measures (detects) the curl state of the sheet is disposed in the double-sided conveyance unit 8, but the sheet curl measurement unit 70 is a sheet P that is conveyed to the sheet conveyance device 50. It may be placed anywhere as long as it is on the transport system path through which. In particular, if it is installed in the transport path immediately before the sheet transport apparatus 50 through which both the sheet P transported from the sheet cassettes C1 and C2 and the sheet P that has passed through the double-side transport unit 8 pass, the following effects can be obtained. . That is, even with respect to the sheet curl generated in the sheet cassettes C1 and C2, the conveyance path of the sheet conveyance device 50 can be selected according to the curl direction, so that the sheet alignment can be performed with higher accuracy.

  Further, the sheet conveying apparatus 50 is configured to have a plurality of sheet conveying paths by providing a plurality (three in this embodiment) of oblique conveying paths provided with a pair of inclined feeding rollers. However, the same effect can be obtained by providing a single oblique conveyance path that can be moved or deformed and having a plurality of oblique conveyance paths by moving or deforming the diagonal conveyance path.

DESCRIPTION OF SYMBOLS 2 ... Intermediate transfer belt, 13 ... Main conveyance path (paper feeding conveyance unit), 15 ... Control unit, 18 ... Image forming device, 20 ... Sheet conveyance device, 23 ... Switching lever (flapper), 25 ... Side guide, 25a ... Reference plane, 30 ... linear conveyance path, 31-33 ... width-adjusting roller (slope feeding roller pair), 40 ... conveyance path (curved conveyance path, first curved conveyance path), 41-43 ... width-adjusting roller (Slip feed roller pair), 50... Sheet transport device, 51... Switching lever (flapper), 60... Transport path (second curved transport path), 61 to 63. ... Curl detection section (sheet curl measurement section), A ... secondary transfer point, P ... sheet

Claims (7)

In a sheet conveying apparatus having a skew correction unit that corrects skew of a conveyed sheet,
The skew correction unit is
A plurality of conveying paths having different curvatures;
Provided in each of the plurality of conveyance paths, the sheets conveyed in the respective conveyance paths are width-adjusted by a width-adjusting roller, and the side edges of the sheets are brought into sliding contact with a reference plane arranged along the sheet conveyance direction. A skew correction mechanism that corrects skew while
A control unit that selects a conveyance path so that the sheet is fed along a conveyance path having a large curvature as the basis weight of the sheet whose skew is corrected is small;
A switching unit that switches the conveyance direction of the sheet so that the sheet is conveyed on the conveyance path selected by the control unit;
A sheet conveying apparatus comprising: The plurality of transport paths branch from the main transport path on the upstream side and are arranged in parallel up and down,
The switching unit includes a switching lever for sending a sheet to the conveyance path selected by the control unit of the branched conveyance path,
The control unit switches the switching lever so that a sheet having a basis weight of a predetermined value or more is guided to a conveyance path having a small curvature, and a sheet having a basis weight less than the predetermined value is guided to a conveyance path having a large curvature,
The sheet conveying apparatus according to claim 1. One of the plurality of conveyance paths is a linear conveyance path.
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is characterized. In a sheet conveying apparatus having a skew correction unit that corrects skew of a conveyed sheet,
The skew correction unit is
A plurality of conveyance paths having different bending directions;
Provided in each of the plurality of conveyance paths, the sheets conveyed in the respective conveyance paths are width-adjusted by a width-adjusting roller, and the side edges of the sheets are brought into sliding contact with a reference plane arranged along the sheet conveyance direction. A skew correction mechanism that corrects skew while
A curl detection unit that is disposed upstream of the conveyance path in the sheet conveyance direction and detects a curl state of the sheet whose skew is corrected,
A control unit that selects a conveyance path having a curvature in the same direction as the curl direction of the sheet detected by the curl detection unit;
A switching unit that switches the conveyance direction of the sheet so that the sheet is conveyed to the conveyance path selected by the control unit;
A sheet conveying apparatus comprising: The plurality of conveyance paths branch from the upstream main conveyance path and are arranged in parallel up and down, and the switching unit is a switching lever for sending a sheet to the conveyance path selected by the control unit of the branched conveyance path The control unit switches the switching lever so as to guide the sheet to a conveyance path having a curvature in the same direction as the direction of the curl detected by the curl detection unit.
The sheet conveying apparatus according to claim 4. Furthermore, a linear conveyance path is provided.
The sheet conveying apparatus according to claim 4, wherein the sheet conveying apparatus is characterized. A sheet conveying apparatus according to any one of claims 1 to 6,
An image forming unit that forms an image on a sheet conveyed by the sheet conveying device;
An image forming apparatus.

Images