Sheet conveyance device and image forming device

Abstract

To provide a sheet conveyance device capable of reducing sheet conveyance failures and an image forming device equipped with the same.SOLUTION: This sheet conveyance device comprises: a conveyance rotor pair that conveys a sheet in a sheet conveying direction; a skew correction unit having first and second butting parts against which the tip of the sheet butts; and a guide that guides the sheet conveyed by the conveyance rotor pair. The guide is disposed between the first and second butting parts in a width direction, and has a guide surface that forms a conveyance path where the sheet passes, a first recess disposed upstream of the first butting part in the sheet conveying direction and at a position overlapping it in the width direction, and recessed on a side opposite the conveyance path with respect to the guide surface, and a second recess disposed upstream of the second butting part in the sheet conveying direction and at a position overlapping it in the width direction, and recessed on a side opposite the conveyance path with respect to the guide surface.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a sheet conveying device for conveying a sheet and an image forming apparatus including the same.

Background Art

[0002] Conventionally, an image forming apparatus has been proposed that corrects skewing of a sheet by abutting the leading end of the sheet conveyed by a pair of pre-registration rollers against the nip portion of a pair of registration rollers that are stopped in rotation and forming a loop in the sheet (see Patent Document 1). This image forming apparatus has a separating means for separating the pair of pre-registration rollers from each other.

[0003] The skewed-corrected sheet is conveyed by the pair of pre-registration rollers toward the secondary transfer portion. At this time, a force to return the skewing is generated in the sheet due to the loop reaction force. For this reason, the image forming apparatus reduces the loop pressure generated in the sheet by separating (releasing) the nip portion of the pair of pre-registration rollers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the image forming apparatus described in Patent Document 1 brings the pair of pre-registration rollers into contact again after releasing the nip portion of the pair of pre-registration rollers. At this time, the posture of the sheet may not be stable, and there is a risk of conveyance failure such as slip occurring in the pair of pre-registration rollers.

[0006] An object of the present invention is to provide a sheet conveying device capable of reducing conveyance failure of a sheet and an image forming apparatus including the same.

Means for Solving the Problems

[0007] The present invention relates to a sheet conveying device, comprising: a pair of conveying rotating bodies that convey a sheet in the sheet conveying direction; a first abutment portion against which the leading edge of the sheet conveyed by the pair of conveying rotating bodies abuts; a second abutment portion positioned at a different location from the first abutment portion in the width direction perpendicular to the sheet conveying direction, and correcting the skewness of the sheet by abutting the leading edge of the sheet together with the first abutment portion; and a guide portion that guides the sheet conveyed by the pair of conveying rotating bodies toward the first abutment portion and the second abutment portion, wherein the guide portion comprises: a guide surface positioned between the first abutment portion and the second abutment portion in the width direction, forming a conveying path through which the sheet passes; a first recess positioned upstream of the first abutment portion with respect to the sheet conveying direction and overlapping with respect to the width direction, and recessed on the opposite side of the conveying path from the guide surface; and a second recess positioned upstream of the second abutment portion with respect to the sheet conveying direction and overlapping with respect to the width direction, and recessed on the opposite side of the conveying path from the guide surface.

[0008] Furthermore, the present invention relates to a sheet conveying device comprising: a pair of conveying rotating bodies that convey a sheet in the sheet conveying direction; a pair of first rotating bodies having a first nip against which the leading edge of the sheet conveyed by the pair of conveying rotating bodies abuts; a pair of second rotating bodies having a second nip positioned at a different location from the pair of first rotating bodies in a width direction perpendicular to the sheet conveying direction, and correcting the skewness of the sheet by abutting the leading edge of the sheet together with the first nip; and a guide section that guides the sheet conveyed by the pair of conveying rotating bodies toward the first nip and the second nip, wherein the guide section has a guide surface that forms a conveying path through which the sheet passes; and a recess positioned between the first nip and the second nip in the width direction, and recessed on the opposite side from the conveying path relative to the guide surface.

[0009] Furthermore, the present invention relates to a sheet conveying device comprising: a pair of conveying rotating bodies that convey a sheet in the sheet conveying direction; a diagonal correction unit having a stopper portion that corrects the diagonal movement of the sheet by abutting the leading edge of the sheet conveyed by the pair of conveying rotating bodies; and a guide unit that guides the sheet conveyed by the pair of conveying rotating bodies toward the stopper portion, wherein the guide unit has a first guide surface that is positioned on one side of the stopper portion in a width direction perpendicular to the sheet conveying direction and forms a conveying path through which the sheet passes; a second guide surface that is positioned on the other side of the stopper portion in the width direction and forms the conveying path; and a recess that is positioned upstream of the stopper portion with respect to the sheet conveying direction and overlapping with respect to the width direction, and is recessed on the opposite side from the conveying path with respect to the first guide surface and the second guide surface. [Effects of the Invention]

[0010] According to the present invention, sheet transport defects can be reduced. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic diagram showing the printer according to the first embodiment. [Figure 2] Front view showing the registration unit. [Figure 3] A cross-sectional view showing the registration unit. [Figure 4] (a) is a cross-sectional view showing the leading edge of the sheet abutting against the sheet contact surface, (b) is a cross-sectional view showing the leading edge of the sheet moving towards the base of the sheet contact surface, and (c) is a cross-sectional view showing the skew correction unit being pushed up. [Figure 5] A cross-sectional view showing a section including the leading edge of the sheet, viewed from the upstream side in the sheet transport direction. [Figure 6] A front view showing a registration unit according to a modified example of the first embodiment. [Figure 7] A cross-sectional view showing the registration unit. [Figure 8](a) is a cross-sectional view showing the state where the tip of the sheet abuts against the sheet contact surface, (b) is a cross-sectional view showing the state where the tip of the sheet has moved to the root portion of the sheet contact surface, and (c) is a cross-sectional view showing the state where the skew correction unit is pushed up. [Figure 9] It is a cross-sectional view showing a cross-section including the tip of the sheet, as viewed from the upstream side in the sheet conveyance direction. [Figure 10] Front view showing a registration unit according to a second embodiment. [Figure 11] Cross-sectional view showing a registration unit. [Figure 12] (a) is a cross-sectional view showing the state where the tip of the sheet abuts against the sheet contact surface, (b) is a cross-sectional view showing the state where the tip of the sheet has moved to the root portion of the sheet contact surface, and (c) is a cross-sectional view showing the state where the skew correction unit is pushed up. [Figure 13] It is a cross-sectional view showing a cross-section including the tip of the sheet, as viewed from the upstream side in the sheet conveyance direction. [Figure 14] Front view showing a registration unit according to a third embodiment. [Figure 15] Cross-sectional view showing a registration unit. [Figure 16] (a) is a cross-sectional view showing the state where the tip of the sheet abuts against the conveyance nip, (b) is a cross-sectional view showing the state where the tip of the sheet is pushed into the concave portion by the convex portion, and (c) is a cross-sectional view showing the state where the sheet is conveyed by the registration roller pair. [Figure 17] It is a cross-sectional view showing a cross-section including the tip of the sheet, as viewed from the upstream side in the sheet conveyance direction.

Mode for Carrying Out the Invention

[0012] <First Embodiment> 〔Overall Configuration〕 First, the first embodiment of the present invention will be described. The printer 1 as an image forming apparatus is a laser beam printer of an electrophotographic system that forms a monochrome toner image. In the following description, the sheet S is what an image is formed on by the printer 1, and includes, for example, paper, OHT sheets, and the like.

[0013] As shown in FIG. 1, the printer 1 has a feeding unit 30 that feeds the loaded sheet, a sheet conveyance device 90 that conveys the sheet, an image forming unit 60 that forms an image on the sheet fed by the feeding unit 30, and a control unit 95. Further, the printer 1 has a fixing device 7 that fixes the image transferred onto the sheet, and a discharge roller pair 8 that can discharge the sheet to a discharge tray 9.

[0014] When an image forming job is output to the printer 1, an image forming process by the image forming unit 60 is started based on the image information input from an external computer or the like connected to the printer 1. The image forming unit 60 as an image forming section includes a laser scanner 62, a process cartridge P having a photosensitive drum 61, and a transfer roller 631. Around the photosensitive drum 61, a charging roller, a developing roller, and the like (not shown) are provided. The photosensitive drum 61 and the transfer roller 631 form a transfer nip T1.

[0015] The laser scanner 62 irradiates the photosensitive drum 61 with laser light based on the input image information. At this time, the photosensitive drum 61 is pre-charged by a charging roller, and an electrostatic latent image is formed on the photosensitive drum 61 when irradiated with the laser light. Then, this electrostatic latent image is developed by a developing roller, and a monochrome toner image is formed on the photosensitive drum 61.

[0016] In parallel with the image forming process described above, sheets S are fed from the feeding unit 30. The feeding unit 30 includes a cassette 2 that can be pulled out and attached to the main body 1A of the printer 1, a feeding roller 31, and a pair of separating rollers 32. The sheets S contained in the cassette 2 are fed by the feeding roller 31, and the sheets S fed by the feeding roller 31 are separated one by one by the pair of separating rollers 32.

[0017] Furthermore, the cassette 2 may be provided with an intermediate plate capable of supporting and raising / lowering the sheet. For example, when an image forming job is input, the intermediate plate may be raised, bringing the sheet supported by the intermediate plate into contact with the feed roller. In addition, one of the separation roller pair 32 may be a pad or the like, and a torque limiter system or retard roller system can be applied.

[0018] The sheet S, which is fed from the feeding unit 30 and transported by the sheet transport device 90, has the toner image on the photosensitive drum 61 transferred to it at the transfer nip T1 by an electrostatic load bias applied to the transfer roller 631. The remaining toner on the photosensitive drum 61 is collected by a cleaning blade (not shown). The sheet S, on which the toner image has been transferred, is subjected to predetermined heat and pressure by the fixing film 71 and pressure roller 72 of the fixing device 7, causing the toner to melt and solidify (fix) to it. A heating element such as a ceramic heater is arranged inside the fixing film 71. The sheet S that has passed through the fixing device 7 is discharged to the discharge tray 9 by the discharge roller pair 8.

[0019] When forming images on both sides of a sheet S, the sheet S with the image formed on the first side is switched back by the reversing roller pair 35 and transported to the double-sided transport path CP2. The sheet S transported along the double-sided transport path CP2 is then transported again to the transfer nip T1 by the sheet transport device 90, where an image is formed on the second side and the sheet S is discharged to the discharge tray 9.

[0020] [Sheet transport device] Next, the sheet conveying device 90 will be described with reference to Figures 1 to 3. As shown in Figure 1, the sheet conveying device 90 includes a conveying unit 4 and a registration unit 5. The conveying unit 4 has a pair of conveying rollers 41, which are a pair of conveying rotating bodies that convey the sheets S conveyed by the separation roller pair 32 to the registration unit 5.

[0021] As shown in Figures 2 and 3, the registration unit 5 includes a plurality of registration roller pairs 51, a registration frame 52, an opposing guide 54, a downstream guide 55, and a skew correction unit 53. The registration frame 52, the opposing guide 54, and the downstream guide 55 form a transport path CP1 through which the sheet S passes, and the sheet S is transported through the transport path CP1 to the transfer nip T1. The opposing guide 54 and the downstream guide 55 are held by the registration frame 52 and the side plate 56.

[0022] In this embodiment, five registration roller pairs 51 are arranged in parallel in the width direction W, perpendicular to the sheet conveying direction CD. Each registration roller pair 51, as a rotating body pair, consists of a registration roller 511 and a registration roller 512. The registration roller 511 and registration roller 512 form a conveying nip N1 (see Figure 1) that conveys the sheet S. A registration frame 52, which serves as a guide, supports a plurality (five in this embodiment) of registration holders 513 so as to be swingable, and the registration holders 513 rotatably support the registration rollers 512. A spring (not shown) is placed between the registration holders 513 and the registration frame 52, and the spring presses the registration rollers 512 against the registration rollers 511.

[0023] [Skew correction unit] Next, the skew correction unit 53 will be described with reference to Figures 2 to 5. As shown in Figures 2 and 3, the skew correction unit 53, as a skew correction section, has a plurality of skew correction members 531 and a connecting member 532 that connects these skew correction members 531. In this embodiment, four skew correction members 531 are arranged in parallel in the width direction W, and each skew correction member 531 is positioned so as to be sandwiched between two pairs of registration rollers 51 in the width direction W. That is, the pairs of registration rollers 51 and the skew correction members 531 are arranged alternately in the width direction W.

[0024] Furthermore, the registration frame 52 has multiple guide surfaces 52a that are spaced apart in the width direction W and form a transport path CP1, and the skew correction member 531 and the registration roller 512 are arranged in these gaps. For this reason, a guide surface 52a is arranged between the skew correction member 531 and the registration roller 512. Each guide surface 52a is arranged to overlap when viewed in the width direction W.

[0025] The skew correction unit 53 is supported so as to be able to swing with respect to the registration frame 52 around the pivot axis 53P, and is positioned in the standby position shown in Figure 3 by a stopper and spring (not shown). That is, the multiple skew correction members 531 and connecting members 532 swing together around the pivot axis 53P. The position of the skew correction member 531 at this time is also referred to as the standby position. The skew correction member 531 has a main body portion 531b and a sheet contact surface 531a extending from the main body portion 531b, to which the leading edge of the sheet S passing through the transport path CP1 can make contact.

[0026] The sheet contact surface 531a protrudes into the transport path CP1 when the skew correction member 531 is in contact with it, and is positioned upstream of the transport nip N1 of the registration roller pair 51 in the sheet transport direction CD. At this time, the sheet contact surface 531a, as an inclined surface, is inclined upstream in the sheet transport direction CD as it approaches the tip, i.e., as it moves away from the main body portion 531b, when viewed in the width direction W. In other words, the sheet contact surface 531a is inclined so as it moves downstream in the sheet transport direction CD, it approaches the recess 52b described later in the thickness direction of the sheet. Also, when viewed in the width direction W, the tip 531c of the sheet contact surface 531a is located inside the opposing guide 54, which is further inside than the opposing guide surface 54a, and the base portion 531d of the sheet contact surface 531a is located inside the registration frame 52, which is further inside than the guide surface 52a. The opposing guide surfaces 54a and 52a of the opposing guide 54, which serves as an opposing guide section, form a part of the transport path CP1.

[0027] More specifically, the registration frame 52 has recesses 52b formed at positions that overlap with each oblique correction member 531 in the width direction W, and the recesses 52b are recessed on the opposite side of the transport path CP1 relative to the guide surface 52a. The base portion 531d of the sheet contact surface 531a extends into the interior of the recesses 52b. The recesses 52b extend at least upstream from a position that overlaps with the base portion 531d of the sheet contact surface 531a in the sheet transport direction CD, but may also extend downstream from the position that overlaps with the base portion 531d. The recesses 52b can be any configuration such as holes, openings, and grooves, as long as they are formed so that a space communicates with the inside of the registration frame 52 more than the guide surface 52a when viewed in the width direction W.

[0028] Furthermore, of the multiple skew correction members 531, the sheet contact surfaces 531a located on the outside of the conveying path CP1 in the width direction W are positioned further upstream in the sheet conveying direction CD than those located on the inside. In this embodiment, since four skew correction members 531 are provided, the two sheet contact surfaces 531a located on the outside in the width direction W are designated as the third abutment portion and the fourth abutment portion. In this case, the third abutment portion and the fourth abutment portion are positioned further upstream in the sheet conveying direction CD than the two sheet contact surfaces 531a designated as the first abutment portion and the second abutment portion, which are located on the inside in the width direction W.

[0029] Next, the operation of the skew correction unit 53 will be explained using Figures 4(a) to 5. As shown in Figure 4(a), the sheet S transported by the transport unit 4 enters the registration unit 5 along the transport path CP1. The leading edge Sa of the sheet S then comes into contact with one of the sheet contact surfaces 531a of the plurality of skew correction members 531 located in standby positions.

[0030] At this time, if the sheet S is transported in an oblique position, the leading edge of the sheet S on the side that is ahead in the width direction W will first come into contact with the sheet contact surface 531a. Then, the sheet S will pivot around the point of contact with the sheet contact surface 531a that it first came into contact with, and will come into contact with the sheet contact surfaces 531a of the other oblique correction members 531.

[0031] Furthermore, as shown in Figure 4(b), the sheet contact surface 531a is inclined downstream in the sheet transport direction CD as it moves from the tip 531c towards the base 531d. Therefore, the tip Sa of the sheet S that abuts against the sheet contact surface 531a is guided toward the base 531d. Thus, the tip Sa of the sheet S moves toward the base 531d while pivoting. The skew of the sheet S is corrected when the tip Sa of the sheet S abuts against at least two of the sheet contact surfaces 531a of the multiple (four) skew correction members 531. Note that at the point when the skew of the sheet S is corrected, the biasing force of the spring that holds the skew correction unit 53 in the standby position is greater than the pressing force that the sheet S exerts on the sheet contact surface 531a.

[0032] As described above, a recess 52b is formed in the registration frame 52 at a position that overlaps with the skew correction member 531 in the width direction W. Therefore, the leading edge Sa of the sheet S, whose skew has been corrected, has a region that abuts against the guide surface 52a and a region that enters the recess 52b, and these regions are located at different positions in the thickness direction of the sheet.

[0033] Figure 5 is a cross-section of the sheet S including its leading edge Sa, viewed from the upstream side in the sheet transport direction CD. As shown in Figure 5, the leading edge Sa of the sheet S alternates in the width direction W between a region that abuts the guide surface 52a and a region that enters the recess 52b.

[0034] For example, when the two central sheet contact surfaces 531a, 531a in the width direction W are designated as the first abutment and the second abutment, the tip Sa of the sheet S abuts against these first and second abutment, correcting the skewness of the sheet S. The tip Sa of the sheet S is then sandwiched between the guide surface 52a, which is positioned between the sheet contact surfaces 531a, 531a in the width direction W, and the sheet contact surfaces 531a, 531a, causing the tip Sa of the sheet S to take on a wavy shape. The tip Sa enters the recesses 52b, 52b, which are the first and second recesses, respectively, located at positions that overlap with the sheet contact surfaces 531a, 531a in the width direction W.

[0035] Furthermore, for example, if one of the two sheet contact surfaces 531a, 531a on the central side in the width direction W is designated as a stopper, and the stopper is sufficiently long in the width direction W, the skewness of the sheet S is corrected by the stopper alone. The leading edge Sa of the sheet S is sandwiched between the recess 52b, which is located in a position that overlaps with the sheet contact surface 531a (the stopper) in the width direction W, and the guide surfaces 52a, 52a, which are the first guide surface and the second guide surface, respectively, which are located on one side and the other side of the recess 52b or the stopper in the width direction W. The leading edge Sa of the sheet S enters the recess 52b and takes on a wavy shape.

[0036] In this way, by sandwiching the leading edge Sa of the sheet S between the guide surface 52a and the sheet contact surface 531a, which are misaligned in the width direction W and the thickness direction of the sheet, the leading edge Sa of the sheet S takes on a wavy shape. As mentioned above, the sheet contact surface 531a of the oblique correction member 531 is located further upstream in the sheet transport direction CD the further it is positioned on the outside of the transport path CP1 in the width direction W, making it easier to sandwich the sheet all the way to the end with the guide surface 52a and the sheet contact surface 531a. Therefore, it is possible to make the entire sheet wavy.

[0037] Furthermore, since the sheet S is transported by the transport unit 4 even while its movement in the sheet transport direction CD is restricted by the sheet contact surface 531a, it forms a loop upstream of the tip Sa in the sheet transport direction CD. Conventionally, the loop formed on the sheet S comes into contact with the transport guide (e.g., registration frame 52), and the reaction force is used to push up the oblique correction unit 53 with the tip Sa of the sheet S.

[0038] However, the size of the loop formed on the sheet S is larger on the side that first contacts the sheet contact surface 531a in the width direction W than on the side that last contacts it. And because the size of the loop formed on the sheet S is different in the width direction W, the reaction force that the sheet S receives from the transport guide is different in the width direction W. As a result, after the skew correction unit 53 is pushed up, the difference in the reaction force received in the width direction W causes the skew of the sheet S to gradually return to normal (hereinafter referred to as skew return).

[0039] However, in this embodiment, as described above, by causing the leading edge Sa of the sheet S to undulate, the second moment of area of ​​the sheet S increases, and its rigidity is temporarily improved. Therefore, even when the sheet S is transported by the transport unit 4 with the leading edge Sa blocked by the sheet contact surface 531a, loops are less likely to form in the sheet S. Thus, as shown in Figure 4(c), the sheet S does not have loops that come into contact with the registration frame 52 or the opposing guide 54, and the sheet S can push up the skew correction unit 53 solely by the rigidity of the sheet S itself.

[0040] When the skew correction unit 53 rotates from its standby position around the pivot axis 53P, the sheet contact surface 531a retracts from the transport path CP1, allowing the sheet S to pass through the transport path CP1. As a result, the sheet S passes through the registration unit 5 and is transported downstream in the sheet transport direction CD. While the sheet S is passing through the registration unit 5, the skew correction member 531 is biased by a spring (not shown) and slides against the surface of the sheet S. When the rear end of the sheet S passes the skew correction member 531, the skew correction member 531 returns to its standby position by the spring.

[0041] As described above, in this embodiment, by making the leading edge Sa of the sheet S wavy, the rigidity of the sheet S itself is temporarily improved, and the loops formed on the sheet S during skew correction can be reduced. This reduces skew reversal and reduces transport defects such as sheet skew. Furthermore, it improves the accuracy of printed images and allows for the acquisition of good results. In particular, sheets with a small basis weight, such as thin paper, tend to have larger loops formed during skew correction, but according to this embodiment, skew can be corrected well regardless of the basis weight of the sheet. Moreover, since this embodiment has a simple configuration, sheet skew can be corrected with an inexpensive configuration.

[0042] <Variation> Next, a modified example of the first embodiment will be described with reference to Figures 6 to 9. Note that components similar to those in the first embodiment will be omitted from the illustration or will be described using the same reference numerals in the figures.

[0043] In the first embodiment, a plurality of registration rollers 512 were each independently held in a swingable manner by a registration holder 513. As shown in Figures 6 and 7, the registration unit 5A of this modified example has a single registration roller shaft 514 supported by a registration frame 52. A plurality (five in this modified example) of registration rollers 512 are rotatably supported on the registration roller shaft 514. The registration roller shaft 514 is biased toward the registration roller 511 by a biasing member (not shown).

[0044] The skew correction unit 57, which serves as the skew correction section, comprises a plurality (four in this embodiment) of skew correction members 571 arranged in parallel in the width direction W, and a connecting member 572 that connects these skew correction members 571. The skew correction unit 57 is supported so as to be rotatable around the registration roller shaft 514. The skew correction unit 57 only needs to be rotatably supported on the rotation axis of one of the rotating bodies of the registration roller pair 51, or it may be rotatably supported on the rotation axis of the registration roller 512.

[0045] The operation of the skew correction unit 57 is the same as that of the skew correction unit 53 in the first embodiment. As shown in Figure 8(a), the sheet S conveyed by the transport unit 4 enters the registration unit 5A along the transport path CP1. The leading edge Sa of the sheet S then comes into contact with one of the sheet contact surfaces 571a of the plurality of skew correction members 571 located in standby positions.

[0046] At this time, if the sheet S is transported in an oblique position, the leading edge of the sheet S on the side that is ahead in the width direction W will first come into contact with the sheet contact surface 571a. Then, the sheet S will rotate around the point of contact with the sheet contact surface 571a that it first came into contact with, and will come into contact with the sheet contact surfaces 571a of the other oblique correction members 571.

[0047] Furthermore, as shown in Figure 8(b), the sheet contact surfaces 571a, which serve as the abutment portion, the first abutment portion, and the second abutment portion, are inclined toward the downstream direction CD in the sheet transport direction as they move from the tip to the base. Therefore, the tip Sa of the sheet S that abuts against the sheet contact surface 571a is guided toward the base. Thus, the tip Sa of the sheet S moves toward the base of the sheet contact surface 571a while pivoting. The skew of the sheet S is corrected when the tip Sa of the sheet S abuts against at least two of the sheet contact surfaces 571a of the multiple (four) skew correction members 571.

[0048] As described above, a recess 52b is formed in the registration frame 52 at a position that overlaps with the skew correction member 571 in the width direction W. Therefore, the leading edge Sa of the sheet S, whose skew has been corrected, has a region that abuts against the guide surface 52a and a region that enters the recess 52b, and these regions are located at different positions in the thickness direction of the sheet.

[0049] Figure 9 is a cross-section of the sheet S including its leading edge Sa, viewed from the upstream side in the sheet transport direction CD. As shown in Figure 9, the leading edge Sa of the sheet S alternates in the width direction W between the area in contact with the guide surface 52a and the area that enters the recess 52b. In this way, the leading edge Sa of the sheet S is sandwiched between the guide surface 52a and the sheet contact surface 571a, which are misaligned in the width direction W and the thickness direction of the sheet, resulting in a wavy shape at the leading edge Sa of the sheet S.

[0050] By causing the leading edge Sa of the sheet S to undulate, the second moment of area of ​​the sheet S increases, temporarily improving its rigidity. Therefore, even when the sheet S is transported by the transport unit 4 with the leading edge Sa blocked by the sheet contact surface 571a, loops are less likely to form on the sheet S. Thus, as shown in Figure 8(c), the sheet S does not have loops that come into contact with the registration frame 52 or the opposing guide 54, and the sheet S can push up the skew correction unit 57 solely by the rigidity of the sheet S itself.

[0051] When the skew correction unit 57 rotates from its standby position around the registration roller shaft 514, the sheet contact surface 571a retracts from the transport path CP1, allowing the sheet S to pass through the transport path CP1. As a result, the sheet S passes through the registration unit 5A and is transported downstream in the sheet transport direction CD. While the sheet S is passing through the registration unit 5A, the skew correction member 571 is biased by a spring (not shown) and slides against the surface of the sheet S. When the rear end of the sheet S passes the skew correction member 571, the skew correction member 571 returns to its standby position by the spring.

[0052] As described above, in this embodiment, by making the leading edge Sa of the sheet S wavy, the rigidity of the sheet S itself is temporarily improved, and the loops formed on the sheet S during skew correction can be reduced. This reduces skew reversal and reduces transport defects such as sheet skew. Furthermore, it improves the accuracy of printed images and allows for the acquisition of good results. In particular, sheets with a small basis weight, such as thin paper, tend to have larger loops formed during skew correction, but according to this embodiment, skew can be corrected well regardless of the basis weight of the sheet. Moreover, since this embodiment has a simple configuration, sheet skew can be corrected with an inexpensive configuration.

[0053] <Second Embodiment> Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment in the pressure configuration of the registration roller and the configuration of the skew correction unit. For this reason, the same configuration as in the first embodiment will be omitted from the illustration or will be described using the same reference numerals in the illustration.

[0054] [Registration Unit] As shown in Figures 10 and 11, the registration unit 10 according to this embodiment includes a plurality of registration roller pairs 51 and a skew correction unit 103. Five registration roller pairs 51 are arranged side by side in the width direction W perpendicular to the sheet transport direction CD. Each registration roller pair 51 consists of a registration roller 511 and a registration roller 512. The registration roller 511 and registration roller 512 form a transport nip N1 (see Figure 1) that transports the sheet S.

[0055] A registration holder 1013 is linearly supported on the registration frame 52, and the registration holder 1013 rotatably supports a plurality (five in this embodiment) of registration rollers 512. The registration rollers 512 are pressed against registration rollers 511 by a spring (not shown) that biases the registration holder 1013.

[0056] [Skew correction unit] Next, the skew correction unit 103 will be described with reference to Figures 10 to 13. As shown in Figures 10 and 11, the skew correction unit 103, as a skew correction section, has a plurality of skew correction members 1031 and a shaft member 1032 that connects these skew correction members 1031. In this embodiment, four skew correction members 1031 are arranged in parallel in the width direction W, and each skew correction member 1031 is positioned so as to be sandwiched between two pairs of registration rollers 51 in the width direction W. That is, the pairs of registration rollers 51 and the skew correction members 1031 are arranged alternately in the width direction W.

[0057] Furthermore, the registration frame 52 has a plurality of guide surfaces 52a provided with gaps between them in the width direction W, and the skew correction member 1031 and the registration roller 512 are arranged in these gaps. For this reason, the guide surface 52a is positioned between the skew correction member 1031 and the registration roller 512.

[0058] The skew correction unit 103 is rotatably supported on the registration frame 52 with respect to the shaft member 1032 and is positioned in the standby position shown in Figure 11 by a stopper and spring (not shown). In this embodiment, the skew correction unit 103 is formed symmetrically with respect to the shaft member 1032, so it returns to the same orientation, i.e., the standby position, every 120-degree rotation. Hereinafter, the position of the skew correction unit 103, including the position rotated 120 degrees from the standby position (first standby position) to the second standby position, and the position rotated another 120 degrees to the third standby position, will all be referred to as the standby position. The position of the skew correction member 1031 when the skew correction unit 103 is in the standby position will also be referred to as the standby position. The skew correction member 1031 has a main body portion 1031b and three sheet contact surfaces 1031a extending from the main body portion 1031b, to which the leading edge of the sheet S passing through the transport path CP1 can make contact.

[0059] The sheet contact surface 1031a protrudes into the transport path CP1 when the skew correction member 1031 is in contact position, and is positioned upstream of the transport nip N1 of the registration roller pair 51 in the sheet transport direction CD. At this time, the sheet contact surface 1031a, as the abutment portion, first abutment portion, and second abutment portion, is inclined upstream in the sheet transport direction CD as it approaches the tip, i.e., as it moves away from the main body portion 1031b, when viewed in the width direction W. Also, when viewed in the width direction W, the tip 1031c of the sheet contact surface 1031a is located inside the opposing guide 54, and the base portion 531d of the sheet contact surface 1031a is located inside the registration frame 52 beyond the guide surface 52a.

[0060] More specifically, the registration frame 52 has recesses 52b formed at positions that overlap with each oblique correction member 1031 in the width direction W. The recesses 52b extend upstream from a position that overlaps with the base portion 1031d of the sheet contact surface 1031a in the sheet transport direction CD, but may also extend downstream from the position that overlaps with the base portion 531d. The recesses 52b can be any configuration such as holes, openings, and grooves, as long as they are formed so that a space communicates with the inside of the registration frame 52 more than the guide surface 52a when viewed in the width direction W.

[0061] Furthermore, of the multiple skew correction members 1031, the sheet contact surfaces 1031a located on the outside of the conveyor path CP1 in the width direction W are located further upstream in the sheet conveying direction CD than those located on the inside. In this embodiment, since four skew correction members 1031 are provided, the two sheet contact surfaces 1031a located on the outside in the width direction W are located further upstream in the sheet conveying direction CD than the two sheet contact surfaces 1031a located on the inside.

[0062] Next, the operation of the skew correction unit 103 will be explained using Figures 12(a) to 13. As shown in Figure 12(a), the sheet S transported by the transport unit 4 enters the registration unit 10 along the transport path CP1. The leading edge Sa of the sheet S then comes into contact with one of the sheet contact surfaces 1031a of the multiple skew correction members 1031 located in standby positions.

[0063] At this time, if the sheet S is transported in an oblique position, the leading edge of the sheet S on the side that is ahead in the width direction W will first come into contact with the sheet contact surface 1031a. Then, the sheet S will rotate around the point of contact with the sheet contact surface 1031a that it first came into contact with, and will come into contact with the sheet contact surfaces 1031a of the other oblique correction members 1031.

[0064] Furthermore, as shown in Figure 12(b), the sheet contact surface 1031a is inclined downstream in the sheet transport direction CD as it moves from the tip 1031c towards the base 531d. Therefore, the tip Sa of the sheet S that abuts against the sheet contact surface 1031a is guided toward the base 1031d. Thus, the tip Sa of the sheet S moves toward the base 1031d while pivoting. The skew of the sheet S is corrected when the tip Sa of the sheet S abuts against at least two of the sheet contact surfaces 1031a of the multiple (four) skew correction members 1031. Note that at the point when the skew of the sheet S is corrected, the biasing force of the spring that holds the skew correction unit 103 in the standby position is greater than the pressing force that the sheet S exerts on the sheet contact surface 1031a.

[0065] As described above, a recess 52b is formed in the registration frame 52 at a position that overlaps with the skew correction member 1031 in the width direction W. Therefore, the leading edge Sa of the sheet S, whose skew has been corrected, has a region that abuts against the guide surface 52a and a region that enters the recess 52b, and these regions are located at different positions in the thickness direction of the sheet.

[0066] Figure 13 is a cross-section of the sheet S including its leading edge Sa, viewed from the upstream side in the sheet transport direction CD. As shown in Figure 13, the leading edge Sa of the sheet S alternates in the width direction W between the area in contact with the guide surface 52a and the area that enters the recess 52b. In this way, the leading edge Sa of the sheet S is sandwiched between the guide surface 52a and the sheet contact surface 1031a, which are misaligned in the width direction W and the thickness direction of the sheet, resulting in the leading edge Sa of the sheet S having a wavy shape. As mentioned above, the sheet contact surface 1031a of the skew correction member 1031 is located further upstream in the sheet transport direction CD the further it is positioned on the outside of the transport path CP1 in the width direction W, making it easier to sandwich the sheet all the way to the end between the guide surface 52a and the sheet contact surface 1031a. Therefore, it is possible to make the entire sheet wavy.

[0067] Furthermore, since the sheet S is transported by the transport unit 4 even while its movement in the sheet transport direction CD is restricted by the sheet contact surface 1031a, it forms a loop upstream of the tip Sa in the sheet transport direction CD. However, by causing the tip Sa of the sheet S to undulate, the second moment of area of ​​the sheet S increases, and its rigidity is temporarily improved. Therefore, even if the sheet S is transported by the transport unit 4 with the tip Sa blocked by the sheet contact surface 1031a, it is difficult for a loop to form in the sheet S. Thus, as shown in Figure 12(c), the sheet S can push up the skew correction unit 103 by the rigidity of the sheet S itself, without the loop contacting the registration frame 52 or the opposing guide 54, etc.

[0068] When the skew correction unit 103 rotates from its standby position around the shaft member 1032, the sheet contact surface 1031a retracts from the transport path CP1, allowing the sheet S to pass through the transport path CP1. As a result, the sheet S passes through the registration unit 10 and is transported downstream in the sheet transport direction CD. While the sheet S is passing through the registration unit 10, the skew correction member 1031 is biased by a spring (not shown) and slides against the surface of the sheet S. When the rear end of the sheet S passes the skew correction member 1031, the skew correction member 1031 moves to the next standby position by the spring.

[0069] As described above, in this embodiment, by making the leading edge Sa of the sheet S wavy, the rigidity of the sheet S itself can be temporarily improved, and the loops formed on the sheet S during skew correction can be reduced. This reduces skew reversal and reduces transport defects such as sheet skew. Furthermore, it improves the accuracy of printed images and allows for the acquisition of good results. In particular, sheets with a small basis weight, such as thin paper, tend to have larger loops formed during skew correction, but according to this embodiment, skew can be corrected well regardless of the basis weight of the sheet.

[0070] Furthermore, because this embodiment has a simple configuration, sheet skew can be corrected with an inexpensive setup. Also, the skew correction unit 103 rotates in only one direction when pressed against the leading edge Sa of the sheet S. Therefore, as soon as the rear end of the sheet S passes the first sheet contact surface 1031a, the second sheet contact surface 1031a immediately protrudes into the transport path CP1, preparing for skew correction of subsequent sheets. Thus, the spacing between sheets being transported continuously, i.e., the gap between sheets, can be reduced, improving throughput.

[0071] <Third Embodiment> Next, a third embodiment of the present invention will be described. The third embodiment differs from the first embodiment in the pressure configuration of the registration roller and the configuration of the skew correction unit. For this reason, the same configuration as in the first embodiment will be omitted from the illustration or will be described using the same reference numerals in the illustration.

[0072] [Registration Unit] As shown in Figures 14 and 15, the registration unit 11 as a diagonal correction unit according to this embodiment has a plurality of registration roller pairs 51 as a first rotating body pair and a second rotating body pair, and a swing guide 114. Five registration roller pairs 51 are arranged side by side in the width direction W perpendicular to the sheet conveying direction CD. Each registration roller pair 51 consists of a registration roller 511 and a registration roller 512. The registration roller 511 and registration roller 512 form a conveying nip N1 as a first nip and a second nip for conveying the sheet S.

[0073] A registration frame 52 supports one registration roller shaft 514, and a plurality (five in this modified example) of registration rollers 512 are rotatably supported on the registration roller shaft 514. The registration roller shaft 514 is biased toward the registration roller 511 by a biasing member (not shown).

[0074] In this embodiment, there is no diagonal correction member that the leading edge Sa of the sheet S abuts against; the sheet S's diagonal alignment is corrected when its leading edge Sa abuts against the conveying nip N1. In other words, a stop roller system is employed in this embodiment. The drive control of the registration roller 511 is performed by the control unit 95 (see Figure 1).

[0075] The registration frame 52 is provided with gaps between each other in the width direction W and has a plurality of guide surfaces 52a that form a transport path CP1. Recesses 52b and registration rollers 512, similar to those in the first and second embodiments, are arranged in these gaps. Therefore, guide surfaces 52a are arranged between the recesses 52b and the registration rollers 512, and recesses 52b are arranged between two adjacent registration rollers 512.

[0076] A swing guide 114 is supported on the registration frame 52 so as to be able to swing around a swing axis (not shown) extending in the width direction W, and the swing guide 114 is positioned in the standby position shown in Figure 15 by a spring (not shown). When in the standby position, the swing guide 114 has a plurality of (four in this embodiment) protrusions 114a that each enter into a plurality of recesses 52b. The protrusions 114a have an inclined surface 114b positioned upstream of the conveying nip N1 in the sheet conveying direction CD. When viewed in the width direction W, the inclined surface 114b is inclined so that it moves towards the recesses 52b as it moves downstream in the sheet conveying direction CD.

[0077] In this embodiment, four protrusions 114a are formed on a single oscillating guide 114, and the four protrusions 114a oscillate together as a single unit. However, the embodiment is not limited to this configuration. For example, multiple oscillating guides that oscillate separately may be provided, and each oscillating guide may have a protrusion.

[0078] As shown in Figure 16(a), the sheet S, transported by the transport unit 4, enters the registration unit 11 along the transport path CP1. The leading edge Sa of the sheet S then contacts the transport nip N1 of the stationary registration roller pair 51.

[0079] At this time, if the sheet S is being transported at an angle, the leading edge of the sheet S on the side that is ahead in the width direction W will first come into contact with the transport nip N1. Then, the sheet S will rotate around the point of initial contact with the transport nip N1 so that its leading edge Sa follows the shape of the transport nip N1.

[0080] Furthermore, as shown in Figure 16(b), the inclined surface 114b of the convex portion 114a of the oscillating guide 114 is inclined toward the concave portion 52b in the thickness direction of the sheet as it moves downstream in the sheet conveying direction CD. Therefore, the leading edge Sa of the sheet S that abuts against the conveying nip N1 is pressed by the convex portion 114a and guided toward the concave portion 52b.

[0081] Therefore, the leading edge Sa of the sheet S, whose skewness is corrected by following the transport nip N1, has a region that contacts the guide surface 52a and a region that enters the recess 52b, and these regions are located at different positions in the thickness direction of the sheet.

[0082] Figure 17 is a cross-section of the sheet S including its leading edge Sa, viewed from the upstream side in the sheet transport direction CD. As shown in Figure 17, the leading edge Sa of the sheet S alternates in the width direction W between a region that abuts the guide surface 52a and a region that enters the recess 52b.

[0083] For example, if two of the central transport nips N1, N1 in the width direction W are designated as the first nip and the second nip, the sheet S's skew is corrected when the tip Sa abuts against these first and second nips. The tip Sa of the sheet S is then sandwiched between the recess 52b, which is positioned between the transport nips N1, N1 in the width direction W, and the transport nips N1, N1, causing the tip Sa of the sheet S to take on a wavy shape. The tip Sa enters the recess 52b.

[0084] In this way, the leading edge Sa of the sheet S is sandwiched between the transport nip N1 and the protrusion 114a, which are misaligned in the width direction W and the thickness direction of the sheet, resulting in the leading edge Sa of the sheet S having a wavy shape.

[0085] Furthermore, since the sheet S is transported by the transport unit 4 even while its movement in the sheet transport direction CD is restricted by the transport nip N1, a loop is formed upstream of the tip Sa in the sheet transport direction CD. However, in this embodiment, as described above, by causing the tip Sa of the sheet S to undulate, the second moment of area of ​​the sheet S increases, and its rigidity is temporarily improved. Therefore, even if the sheet S is transported by the transport unit 4 with the tip Sa blocked by the transport nip N1, a loop is less likely to form in the sheet S. In other words, even if the registration roller pair 51 is stopped for the same amount of time as in the conventional method, a loop is less likely to form in the sheet S in this embodiment than in the conventional method.

[0086] Then, as shown in Figure 16(c), the registration roller pair 51, driven by the control unit 95, transports the sheet S, but at this time, the loop of the sheet S does not come into contact with the registration frame 52 or the swing guide 114. Therefore, the skewed return caused by the reaction force received by the sheet S from the transport guide is reduced, and the skew is corrected well. While the sheet S is passing through the transport nip N1, the swing guide 114 moves so as to be pressed against the surface of the sheet S and open the transport path CP1. That is, the swing guide 114 swings so that the protrusion 114a moves away from the recess 52b. When the rear end of the sheet S passes the protrusion 114a, the swing guide 114 returns to the standby position by the spring.

[0087] As described above, in this embodiment, by making the leading edge Sa of the sheet S wavy, the rigidity of the sheet S itself is temporarily improved, and the loops formed on the sheet S during skew correction can be reduced. This reduces skew reversal and allows for good correction of the sheet's skew. Furthermore, it improves the accuracy of the printed image and allows for the acquisition of good results. In particular, sheets with a small basis weight, such as thin paper, tend to have larger loops formed during skew correction, but according to this embodiment, skew can be corrected well regardless of the sheet's basis weight. Moreover, since this embodiment has a simple configuration, sheet skew can be corrected with an inexpensive configuration.

[0088] In this embodiment, the swing guide 114 was swingably mounted to the registration frame 52, but the embodiment is not limited to this. For example, the swing guide 114 may be mounted linearly relative to the registration frame 52.

[0089] <Other Embodiments> In all of the embodiments described above, the conveying roller pair 41 and the registration roller pair 51 were each composed of rollers, but this is not limited to them. For example, these conveying roller pair 41 and registration roller pair 51 may be partially or entirely composed of other rotating bodies such as belts.

[0090] Furthermore, while the first and second embodiments provided a guide surface 52a and a recess 52b on the registration frame 52, the embodiment is not limited to this. For example, the guide surface 52a and the recess 52b may be provided on a member other than the registration frame 52. Furthermore, in the first embodiment, the skew correction member 531 was supported by the registration frame 52, but it may be supported by other members.

[0091] Furthermore, although the invention has been described using an electrophotographic printer 1 in all of the embodiments described above, the present invention is not limited to this. For example, the present invention can also be applied to an inkjet image forming apparatus that forms an image on a sheet by ejecting ink liquid from a nozzle. In addition, the embodiments and modifications described above may be combined in any way.

[0092] Furthermore, the disclosure of this embodiment includes the following configurations and methods. (Composition 1) A pair of conveying rotating bodies that convey sheets in the sheet conveying direction, A skew correction unit having a first abutment portion against which the leading edge of the sheet conveyed by the conveying rotating body pair abuts, and a second abutment portion positioned at a different location from the first abutment portion in the width direction perpendicular to the sheet conveying direction, and correcting the skew of the sheet by abutting the leading edge of the sheet together with the first abutment portion, The system includes a guide section that guides the sheet conveyed by the aforementioned pair of conveying rotating bodies toward the first abutment section and the second abutment section, The guide portion comprises: a guide surface positioned between the first abutment portion and the second abutment portion in the width direction, forming a transport path through which the sheet passes; a first recess positioned upstream of the first abutment portion with respect to the sheet transport direction and overlapping with respect to the width direction, and recessed on the opposite side of the transport path from the guide surface; and a second recess positioned upstream of the second abutment portion with respect to the sheet transport direction and overlapping with respect to the width direction, and recessed on the opposite side of the transport path from the guide surface. A sheet conveying device characterized by the following features. (Configuration 2) The leading edge of the sheet, which is conveyed by the pair of conveying rotating bodies and abuts against the first and second abutment portions, enters the first and second recesses. A sheet conveying device according to configuration 1, characterized by the features described above. (Composition 3) The diagonal correction unit is biased to a standby position in which the first abutment portion and the second abutment portion protrude into the transport path. The first and second abutment portions are inclined surfaces that, when the oblique correction unit is in the standby position, are inclined so that, when viewed in the width direction, they approach the recess in the thickness direction of the sheet as they move downstream in the sheet conveying direction. A sheet conveying device according to configuration 1 or 2, characterized by the above. (Composition 4) The system includes an opposing guide portion having an opposing guide surface that faces the guide portion and forms the transport path, The first abutment portion and the second abutment portion, when the oblique correction unit is in the standby position, protrude inward from the opposing guide surface and enter the interior of the recess when viewed in the width direction. A sheet conveying device according to configuration 3, characterized by the features described above. (Composition 5) The diagonal correction unit is pivotably supported by the guide unit. A sheet conveying device according to configuration 3 or 4, characterized by the above. (Composition 6) The rotating body for conveying the sheet has a conveying nip positioned downstream of the first and second abutment portions of the oblique correction unit located at the standby position in the sheet conveying direction, and comprises a pair of rotating bodies for conveying the sheet, The oblique correction unit is rotatably supported on the rotation axis of either one of the rotating bodies of the pair of rotating bodies. A sheet conveying device according to configuration 3 or 4, characterized by the above. (Composition 7) The diagonal correction unit is arranged in the width direction so as to sandwich the first abutment unit and the second abutment unit, and has a third abutment unit and a fourth abutment unit that correct the diagonal alignment of the sheet when the leading edge of the sheet conveyed by the conveying rotating body pair abuts against it. The third and fourth abutment portions are located upstream of the first and second abutment portions in the sheet transport direction. A sheet conveying device according to any one of configurations 1 to 6, characterized by the above. (Composition 8) The loops formed in the sheet by being transported by the transport rotating body pair while abutting against the first and second abutment portions do not come into contact with the guide portion. A sheet conveying device according to any one of configurations 1 to 7, characterized by the above. (Composition 9) A pair of conveying rotating bodies that convey sheets in the sheet conveying direction, A diagonal correction unit comprising: a first pair of rotating bodies having a first nip against which the leading edge of the sheet conveyed by the aforementioned pair of rotating bodies abuts; and a second pair of rotating bodies having a second nip positioned at a different location from the first pair of rotating bodies in the width direction perpendicular to the sheet conveying direction, and correcting the diagonal alignment of the sheet by abutting the leading edge of the sheet together with the first nip; The system includes a guide section that guides the sheet conveyed by the aforementioned pair of conveying rotating bodies toward the first nip and the second nip, The guide portion has a guide surface that forms a conveying path through which the sheet passes, and a recess that is positioned between the first nip and the second nip in the width direction and is recessed on the side opposite to the conveying path relative to the guide surface. A sheet conveying device characterized by the following features. (Composition 10) The leading edge of the sheet, which is conveyed by the pair of conveying rotating bodies and abuts against the first nip and the second nip, enters the recess. A sheet conveying device according to configuration 9, characterized by the features described therein. (Composition 11) The aforementioned oblique correction unit is a swing guide that is pivotably mounted and biased to a standby position, and comprises a swing guide having a convex portion that enters the recess in the standby position. A sheet conveying device according to configuration 9 or 10, characterized by the above. (Composition 12) The convex portion has an inclined surface that, when the swing guide is in the standby position, is inclined in the width direction so as it moves downstream in the sheet transport direction, it approaches the concave portion in the sheet thickness direction. A sheet conveying device according to configuration 11, characterized by the features described above. (Composition 13) The swinging guide is pressed by the sheet being conveyed by the first nip and the second nip, causing the convex portion to swing away from the concave portion. A sheet conveying device according to configuration 11 or 12, characterized by the above. (Composition 14) The loops formed in the sheet by being conveyed by the conveying rotating body pair while abutting against the first nip and the second nip do not come into contact with the guide portion. A sheet conveying device according to any one of configurations 9 to 13, characterized by the features described herein. (Composition 15) A pair of conveying rotating bodies that convey sheets in the sheet conveying direction, A diagonal correction unit having a stopper portion that corrects the diagonal alignment of a sheet by causing the leading edge of the sheet conveyed by the aforementioned pair of conveying rotating bodies to abut against it, The system includes a guide section that guides the sheet conveyed by the aforementioned pair of conveying rotating bodies toward the abutment section, The guide portion includes a first guide surface positioned on one side of the abutment portion in the width direction perpendicular to the sheet conveying direction and forming a conveying path through which the sheet passes; a second guide surface positioned on the other side of the abutment portion in the width direction and forming the conveying path; and a recess positioned upstream of the abutment portion with respect to the sheet conveying direction and overlapping with respect to the width direction, and recessed on the opposite side from the conveying path with respect to the first guide surface and the second guide surface. A sheet conveying device characterized by the following features. (Composition 16) The first guide surface and the second guide surface are arranged to overlap when viewed in the width direction. A sheet conveying device according to configuration 15, characterized by the features described above. (Composition 17) The leading edge of the sheet, which is conveyed by the aforementioned pair of rotating conveying bodies and abuts against the abutment portion, enters the recess. A sheet conveying device according to configuration 15 or 16, characterized by the above. (Composition 18) A sheet transport device according to any one of configurations 1 to 17, The system includes an image forming unit that forms an image on a sheet conveyed by the aforementioned sheet conveying device. An image forming apparatus characterized by the following features. [Explanation of Symbols]

[0093] 1: Image forming apparatus (printer) / 11: Skew correction unit (registration unit) / 41: Transfer rotating body pair (transfer roller pair) / 51: Rotating body pair, first rotating body pair, second rotating body pair (registration roller pair) / 52: Guide unit (registration frame) / 52a: Guide surface, first guide surface, second guide surface / 52b: Recess, first recess, second recess / 53, 57, 103: Skew correction unit (skew correction unit) / 54: Opposite Guide section (opposing guide) / 54a: Opposing guide surface / 60: Image forming section (image forming unit) / 114: Oscillating guide / 114a: Convex part / 114b: Inclined surface / 531a, 571a, 1031a: Abutment part, first abutment part, second abutment part, third abutment part, fourth abutment part (sheet contact surface) / CD: Sheet transport direction / CP1: Transport path / N1: Transport nip, first nip, second nip / S: Sheet / Sa: Tip / W: Width direction

Claims

1. a pair of conveying rotary members that convey the sheet in a sheet conveying direction; a skew correction unit including a first abutment surface against which a leading edge of a sheet conveyed by the pair of conveying rotors abuts, and a second abutment surface that is disposed at a position different from the first abutment surface in a width direction perpendicular to the sheet conveying direction and against which the leading edge of the sheet abuts together with the first abutment surface, and is configured so that the leading edge of the sheet abuts against the first abutment surface and the second abutment surface when correcting skew of the sheet; a guide portion that guides the sheet conveyed by the pair of conveying rotary bodies toward the first abutment surface and the second abutment surface, The first abutment surface has a first root portion, The second abutment surface has a second root portion, the guide portion has a guide surface that is disposed between the first abutment surface and the second abutment surface in the width direction and forms a transport path through which a sheet passes; a first recess that is formed in the guide portion and is disposed upstream of the first abutment surface in the sheet transport direction and at a position overlapping with the first abutment surface in the width direction and is recessed on the opposite side of the transport path from the guide surface; and a second recess that is formed in the guide portion and is disposed upstream of the second abutment surface in the sheet transport direction and at a position overlapping with the second abutment surface in the width direction and is recessed on the opposite side of the transport path from the guide surface, the first base portion is located inside the first recessed portion such that the leading end of the sheet enters the first recessed portion when the leading end abuts against both the first abutment surface and the second abutment surface, the second root portion is located inside the second recessed portion such that the leading end of the sheet enters the second recessed portion when the leading end abuts against both the first abutment surface and the second abutment surface. A sheet conveying device comprising:

2. the skew correction unit is biased to a standby position in which the first abutment surface and the second abutment surface protrude into the transport path, the first abutment surface is an inclined surface that is inclined, when viewed in the width direction, so as to approach the first recess in a thickness direction of the sheet toward a downstream in the sheet conveying direction when the skew correction unit is located at the standby position, the second abutment surface is an inclined surface that is inclined, when viewed in the width direction, so as to approach the second recess in a thickness direction of the sheet toward a downstream in the sheet conveying direction when the skew correction unit is located at the standby position.

2. The sheet transport device according to claim 1.

3. A counter guide surface that forms the conveying path together with the guide surface, and a counter guide portion that faces the guide portion, When the skew correction unit is located at the standby position, the first abutment surface protrudes toward an inside of the opposing guide unit further than the opposing guide surface as viewed in the width direction and enters inside the first recess, When the skew correction unit is located at the standby position, the second abutment surface protrudes toward an inside of the opposing guide unit further than the opposing guide surface as viewed in the width direction, and advances into an inside of the second recess.

3. The sheet transport device according to claim 2.

4. The skew correction unit is supported by the guide unit so as to be swingable.

3. The sheet transport device according to claim 2.

5. a conveying nip disposed downstream of the first abutment surface and the second abutment surface of the skew correction unit located at the standby position in the sheet conveying direction, the conveying nip being disposed downstream of the first abutment surface and the second abutment surface of the skew correction unit located at the standby position in the sheet conveying direction, The skew correction unit is supported rotatably around a rotation axis of one of the pair of rotors.

3. The sheet transport device according to claim 2.

6. The skew correction unit has a first abutting member having the first abutting surface, a second abutting member having the second abutting surface, a connecting member connecting the first abutting member and the second abutting member, and a biasing unit biasing the skew correction unit to a standby position so that the first abutting surface and the second abutting surface protrude into the conveying path, the first abutment surface and the second abutment surface are pressed by the leading end of the sheet conveyed by the pair of conveying rotors, and are thereby retracted from the conveying path against the biasing force of the biasing portion.

2. The sheet transport device according to claim 1.

7. the skew correction unit includes a third abutment surface and a fourth abutment surface that are disposed on either side of the first abutment surface and the second abutment surface in the width direction and against which the leading end of the sheet conveyed by the pair of conveying rotating bodies abuts when correcting skew of the sheet, the third abutment surface and the fourth abutment surface are located upstream of the first abutment surface and the second abutment surface in the sheet conveying direction.

2. The sheet transport device according to claim 1.

8. a loop formed in the sheet by being conveyed by the pair of conveying rotating bodies in a state where the sheet abuts against the first abutment surface and the second abutment surface does not abut against the guide portion; 2. The sheet transport device according to claim 1.

9. The skew correction unit is configured to swing around a swing axis, the guide portion is disposed on the same side as the swing shaft with respect to the transport path, an end portion of the first abutting surface opposite to the first base portion is disposed on an opposite side to the swing shaft across the conveying path; an end portion of the second abutting surface opposite to the second base portion is disposed on the opposite side of the transport path from the swing shaft; 2. The sheet transport device according to claim 1.

10. a pair of conveying rotary members that convey the sheet in a sheet conveying direction; a first rotating body pair having a first nip against which a leading edge of a sheet conveyed by the conveying rotating body pair abuts, and a second rotating body pair arranged at a position different from the first rotating body pair in a width direction perpendicular to the sheet conveying direction and having a second nip against which the leading edge of the sheet abuts, the skew correction unit being configured so that the leading edge of the sheet abuts against the first nip and the second nip when correcting skew of the sheet; a guide portion that guides the sheet conveyed by the pair of conveying rotary bodies toward the first nip and the second nip, the guide portion has a guide surface that forms a transport path through which a sheet passes, and a recess that is formed in the guide portion, is disposed upstream of the first nip and the second nip in the sheet transport direction and between the first nip and the second nip in the width direction, and is recessed on an opposite side of the transport path with respect to the guide surface; the recess is configured so that the leading end of the sheet conveyed by the pair of conveying rotary bodies abuts against the first nip and the second nip and enters into the recess. A sheet conveying device comprising:

11. the skew correction unit is a swingable guide that is swingably provided and biased to a standby position, the swingable guide having a convex portion that enters the concave portion at the standby position, The sheet transport device according to claim 10 .

12. the protrusion has an inclined surface that is inclined so as to approach the recess in a thickness direction of the sheet toward a downstream side in the sheet conveying direction when the swing guide is located at the standby position, as viewed in the width direction. The sheet transport device according to claim 11 .

13. the swing guide is pressed by the sheet conveyed by the first nip and the second nip, and swings such that the convex portion is separated from the concave portion. The sheet transport device according to claim 12 .

14. a loop formed in the sheet by being conveyed by the pair of conveying rotating bodies in a state where the sheet abuts against the first nip and the second nip does not abut against the guide portion; The sheet transport device according to claim 10 .

15. a pair of conveying rotary members that convey the sheet in a sheet conveying direction; a skew correction unit having an abutment surface against which a leading edge of the sheet conveyed by the pair of conveying rotary bodies abuts when correcting the skew of the sheet; a guide portion that guides the sheet conveyed by the pair of conveying rotating bodies toward the abutment surface, The abutment surface has a root portion, the guide portion has a first guide surface that is disposed on one side of the abutment surface in a width direction perpendicular to the sheet transport direction and forms a transport path through which the sheet passes, a second guide surface that is disposed on the other side of the abutment surface in the width direction and forms the transport path, and a recess that is formed in the guide portion and is disposed upstream of the abutment surface in the sheet transport direction and at a position that overlaps with the abutment surface in the width direction, and is recessed on the opposite side of the transport path with respect to the first guide surface and the second guide surface, the base portion is located inside the recessed portion such that the leading end of the sheet enters the recessed portion when the leading end abuts against the abutment surface; A sheet conveying device comprising:

16. The first guide surface and the second guide surface are arranged to overlap each other when viewed in the width direction.

16. The sheet transport device according to claim 15.

17. The skew correction unit is configured to swing around a swing axis, the guide portion is disposed on the same side as the swing shaft with respect to the transport path, an end portion of the abutting surface opposite to the base portion is disposed on the opposite side of the swing shaft across the conveying path; 16. The sheet transport device according to claim 15.

18. A sheet transport device according to any one of claims 1 to 17, an image forming unit that forms an image on the sheet transported by the sheet transport device, 1. An image forming apparatus comprising:

Images