Sheet transport device and image forming apparatus equipped therewith

Abstract

The present invention provides a sheet transport device and an image forming apparatus equipped therewith, which maintain the diagonal correction capability of a diagonal correction mechanism using a shutter member while also expanding the design flexibility. [Solution] The sheet conveying device comprises a pair of conveying rollers and a shutter member. The shutter member has a main body formed to be approximately the same diameter as the radius of the drive roller, and a restricting portion projecting radially outward from the outer peripheral edge of the main body to restrict the leading edge of the sheet. The restricting portion has a contact surface against which the leading edge of the sheet abuts, and a locking portion formed at the boundary between the main body and the contact surface to lock the leading edge of the sheet. The shutter members are arranged in n pairs (n is an integer of 2 or more) symmetrically from the inside to the outside in the sheet width direction, and the locking portion of the m-th pair (m is an integer of 1 or more and n-1 or less) of shutter members from the inside in the sheet width direction is formed radially outward compared to the m+1 pair of shutter members adjacent to it on the outside in the sheet width direction.

Description

【Technical Field】 【0001】 The present invention relates to a charging device used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine using an electrophotographic method, and an image forming apparatus including the same. In particular, the present invention relates to a sheet conveying device that conveys a sheet while correcting skew of the sheet, and an image forming apparatus including the same. 【Background Art】 【0002】 In a conventional image forming apparatus, the accuracy of the recording position of an image on a sheet is one of the important factors in maintaining quality in image formation. And in an image forming apparatus, in order to improve the accuracy of the recording position of an image, when the conveyed sheet is skewed, it is necessary to correct the skewed sheet. 【0003】 Conventionally, a method of arranging a registration roller pair in a sheet conveyance path and abutting the leading end of the conveyed sheet against the nip portion of the registration roller pair in a stopped state to correct the skew of the sheet has been common. 【0004】 In recent years, it has been desired that an image forming apparatus be capable of printing on various media. In particular, in order to cope with further resource savings, the demand for printing on sheets (thin paper) having a lower basis weight than conventional ones has been increasing. However, in the conventional correction method using a registration roller pair, local folding may occur at the leading end of a sheet having a small basis weight and low stiffness, and skew correction may not be sufficient in some cases. 【0005】 Therefore, a method of correcting the skew of a sheet while suppressing the occurrence of local deformation of the sheet has been proposed. Patent Document 1 discloses a sheet conveying device including a pair of conveyance rollers and a shutter member. The shutter member abuts against the leading end of the sheet heading toward the nip portion of the pair of conveyance rollers upstream of the nip portion in the sheet conveyance direction, corrects the skew of the conveyed sheet, and then rotates to guide the sheet to the nip portion. 【Prior Art Documents】 [Patent Documents] 【0006】 [Patent Document 1] Japanese Patent Publication No. 2012-76890 [Overview of the project] [Problems that the invention aims to solve] 【0007】 A resist mechanism using shutter material, such as that described in Patent Document 1, has fewer parts and eliminates the need for relatively expensive components such as clutches and iron rollers, making it advantageous in terms of cost and weight compared to a configuration using a pair of resist rollers. 【0008】 However, if the biasing force of the shutter component that corrects the sheet's edge is too strong, the sheet's ability to correct its skew improves, but sheets with low rigidity, such as thin paper or small-sized paper, become more susceptible to damage. On the other hand, if the biasing force of the shutter component is weakened, damage to the sheet is suppressed, but the sheet's ability to correct its skew decreases. In other words, when the biasing force of the shutter component is taken as a design parameter, the aforementioned bending and damage to the sheet and the ability to correct its skew are inversely related, which limits the design freedom. 【0009】 In view of the above problems, the present invention aims to provide a sheet transport device and an image forming apparatus equipped therewith that maintain the diagonal correction capability of a diagonal correction mechanism using a shutter member while also expanding the degree of design freedom. [Means for solving the problem] 【0010】 To achieve the above objective, the first configuration of the present invention is a sheet conveying device comprising a pair of conveying rollers and a shutter member. The pair of conveying rollers has a drive roller and a driven roller that contacts the drive roller with a predetermined pressure to form a nip portion, and conveys a sheet. The shutter member is rotatably supported on the rotation axis of the drive roller and has a main body portion formed to be approximately the same diameter as the radius of the drive roller, and a restricting portion that protrudes radially outward from the outer peripheral edge of the main body portion and contacts the leading edge of the sheet toward the nip portion upstream of the nip portion in the sheet conveying direction to restrict the leading edge of the sheet, and is capable of changing between a first position in which the restricting portion can correct the skew of the sheet, and a second position in which it rotates from the first position to guide the sheet toward the nip portion. The restricting portion has a contact surface against which the leading edge of the sheet abuts when the shutter member is in the first position, and a locking portion formed at the boundary between the main body portion and the contact surface, into which the leading edge of the sheet is locked. The shutter members are arranged in n pairs (where n is an integer of 2 or more) symmetrically from the inside to the outside in the sheet width direction, which is perpendicular to the sheet transport direction. The mth pair (where m is an integer of 1 or more and n-1 or less) of shutter members from the inside in the sheet width direction has its locking portion formed radially outward compared to the m+1th pair of shutter members adjacent to it on the outside in the sheet width direction. 【0011】 According to the first configuration of the present invention, the force (rotational moment) required for the sheet to rotate the shutter member decreases gradually from the outside to the inside in the sheet width direction. This makes it easier to rotate the shutter member on the inside in the sheet width direction when the tip of a small sheet with weak stiffness abuts against it, thus making it easier for the small sheet to pass through the nip and suppressing bending and damage to the small sheet. Therefore, the designable range (operation window) when correcting skew using the shutter member can be widened compared to conventional designs. [Brief explanation of the drawing] 【0012】 [Figure 1] A schematic cross-sectional view showing the overall configuration of an image forming apparatus 100 equipped with the sheet skew correction unit 20 of the present invention. [Figure 2]Partial perspective view of a sheet skew correction unit 20 according to one embodiment of the present invention, viewed from above. [Figure 3] Side cross-sectional view showing the configuration around the first shutter member 30 of the sheet skew correction unit 20 of this embodiment. [Figure 4] A side cross-sectional view showing the behavior of sheet S as it passes through the first shutter member 30, showing the state in which the leading edge of sheet S is in contact with the contact surface 33a of the first shutter member 30. [Figure 5] This figure shows the state in which a predetermined amount of sheet S is transported from the state in Figure 4, and the leading edge of sheet S presses against the locking portion 33b of the first shutter member material 30. [Figure 6] This figure shows the state in which a predetermined amount of sheet S is conveyed from the state in Figure 5, the first shutter member 30 rotates, and the sheet S passes through the nip portion N of the conveying roller pair 21. [Figure 7] Figure 6 shows the state immediately after the sheet S has been conveyed by a predetermined amount and the rear end of the sheet S has passed the nip portion N of the conveyor roller pair 21. [Figure 8] Side cross-sectional view showing the relationship between the locking portion 33b of the first shutter member 30 and the nip tangent L1 of the transport roller pair 21. [Figure 9] Side cross-sectional view showing the relationship between the locking portion 33b of the second shutter member 31 and the nip tangent L1 of the transport roller pair 21. [Modes for carrying out the invention] 【0013】 Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic cross-sectional view showing the configuration of an image forming apparatus 100 equipped with the sheet skew correction unit 20 of the present invention. Inside the main body of the image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the transport direction (left side in Figure 1). These image forming units Pa to Pd are provided to correspond to images of four different colors (cyan, magenta, yellow, and black), and each sequentially forms images of cyan, magenta, yellow, and black through the processes of charging, exposure, development, and transfer, respectively. 【0014】 These image forming sections Pa to Pd are equipped with photoreceptor drums (image carriers) 1a, 1b, 1c, and 1d, which carry visible images (toner images) of each color. An OPC (organic photosensitive layer) is laminated as a photosensitive layer on the surface of the photoreceptor drums 1a to 1d. Furthermore, an intermediate transfer belt 8, which rotates counterclockwise in Figure 1 by a drive motor (not shown), is provided adjacent to each image forming section Pa to Pd. 【0015】 The toner images formed on these photoreceptor drums 1a to 1d are sequentially transferred and superimposed onto an intermediate transfer belt 8 that moves in contact with each photoreceptor drum 1a to 1d. Subsequently, the toner images transferred onto the intermediate transfer belt 8 are secondarily transferred onto a sheet S, which is an example of a recording medium, by a secondary transfer roller 9. Furthermore, the sheet S on which the toner images have been secondarily transferred is discharged from the image forming apparatus 100 after the toner images have been fixed in the fixing unit 13. The image forming process for each photoreceptor drum 1a to 1d is performed while the photoreceptor drums 1a to 1d are rotated clockwise in Figure 1. 【0016】 The sheet S (transfer paper) on which the toner image is secondarily transferred is housed in a paper cassette 16 located at the bottom of the main body of the image forming apparatus 100. The sheet S is transported via the paper feed roller 12 and the sheet skew correction unit 20 to the nip section between the secondary transfer roller 9 and the drive roller 11 of the intermediate transfer belt 8. The intermediate transfer belt 8 is made of a dielectric resin sheet, and a seamless belt is mainly used. In addition, a blade-shaped belt cleaner 19 is positioned downstream of the secondary transfer roller 9 to remove toner and other residues remaining on the surface of the intermediate transfer belt 8. 【0017】 Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photosensitive drums 1a to 1d, there are charging devices 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d, an exposure device 5 for exposing image information onto each photosensitive drum 1a to 1d, developing devices 3a, 3b, 3c, and 3d for forming toner images on the photosensitive drums 1a to 1d, and cleaning devices 7a, 7b, 7c, and 7d for removing the developer (toner) and the like remaining on the photosensitive drums 1a to 1d. 【0018】 When image data is input from a host device such as a personal computer, first, the charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data, and an electrostatic latent image corresponding to the image data is formed on each photosensitive drum 1a to 1d. 【0019】 The developing devices 3a to 3d are each filled with a predetermined amount of a two-component developer containing cyan, magenta, yellow, and black toners. When the ratio of toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of the toner image described later, toner is replenished from the toner containers 4a to 4d to each of the developing devices 3a to 3d. The toner in this developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and adheres electrostatically. Thereby, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed. 【0020】 Then, an electric field is applied at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d by the primary transfer rollers 6a to 6d, and the cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. These four-color images are formed with a predetermined positional relationship determined in advance for forming a predetermined full-color image. Thereafter, in preparation for the formation of a new electrostatic latent image that is subsequently performed, the toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d. 【0021】 The intermediate transfer belt 8 is stretched between the upstream driven roller 10 and the downstream drive roller 11. As the drive roller 11 rotates due to a drive motor (not shown), the intermediate transfer belt 8 begins to rotate counterclockwise, and the sheet S is transported from the resist roller pair 12b to the nip section (secondary transfer nip section) between the drive roller 11 and the secondary transfer roller 9 located adjacent to it at a predetermined timing. As the sheet S passes through the secondary transfer nip section, the toner image on the intermediate transfer belt 8 is secondary transferred onto the sheet S. The sheet S, on which the toner image has been secondary transferred, is transported to the fixing section 13. 【0022】 The sheet S, transported to the fuser unit 13, is heated and pressurized by the fuser roller pair 13a, fixing the toner image to the surface of the sheet S and forming a predetermined full-color image. The sheet S, on which the full-color image has been formed, is then transported in a direction determined by the branching unit 14, which branches in multiple directions, and is discharged into the discharge tray 17 by the discharge roller pair 15 (or after being sent to the double-sided transport path 18 for double-sided printing). 【0023】 Figure 2 is a partial perspective view from above of a sheet skew correction unit 20 according to one embodiment of the present invention. The sheet skew correction unit 20 comprises a transport roller pair 21 and shutter members 30, 31. The transport roller pair 21 consists of a drive roller 21a and a driven roller 21b (see Figure 3). Multiple pairs (three pairs in this embodiment) of the transport roller pair 21 are arranged along the sheet width direction (direction AA' in Figure 2) which is perpendicular to the transport direction of the sheet S. 【0024】 The drive rollers 21a are fixed to the rotating shaft 22 (see Figure 3) at predetermined intervals. The driven rollers 21b are rotatably supported on the rotating shaft 23 (see Figure 3) at positions opposite each of the drive rollers 21a. The rotating shafts 22 and 23 are each supported on the unit housing 20a parallel to the sheet width direction. A drive input gear 27 is fixed to the rotating shaft 22, to which rotational driving force from a drive motor (not shown) is input. 【0025】 The rotating shaft 23 is biased by a coil spring 25 (see Figure 3) in a direction toward the drive roller 21a. As a result, the driven roller 21b is pressed against the drive roller 21a with a predetermined pressing force to form a nip portion N (see Figure 3), and rotates in accordance with the rotation of the drive roller 21a. 【0026】 The shutter members 30 and 31 are positioned at a total of four locations, at both axial ends of each transport roller pair 21. The shutter members 30 and 31 are rotatably supported on the rotation axis 22 of the drive roller 21a. Hereinafter, the pair of shutter members 30 positioned outside the transport roller pair 21 will be distinguished as the first shutter member, and the pair of shutter members 31 positioned between the transport roller pair 21 will be distinguished as the second shutter member. 【0027】 Of the sheets S transported from the paper cassette 16, large sheets (e.g., A4 size) abut against both the outer first shutter member 30 and the inner second shutter member 31 in the sheet width direction. On the other hand, small sheets (e.g., A5 size) abut against only the inner second shutter member 31. 【0028】 Figure 3 is a side cross-sectional view showing the configuration around the first shutter member 30 of the sheet skew correction unit 20 of this embodiment. As shown in Figure 3, the unit housing 20a includes guide sections 28a and 28b that guide the sheet S, which has been transported from the paper cassette 16 (see Figure 1) to the sheet skew correction unit 20, toward the transport roller pair 21. 【0029】 The first shutter member 30 comprises a disc-shaped main body portion 32 formed to have approximately the same diameter as the drive roller 21a, and a restricting portion 33 projecting radially outward from the outer peripheral edge of the main body portion 32. The restricting portion 33 has a contact surface 33a against which the leading edge of the sheet S, guided along the guide portions 28a and 28b, abuts. A locking portion 33b is formed at the boundary (base) between the main body portion 32 and the restricting portion 33, into which the leading edge of the sheet S is locked. 【0030】 When the sheet S is not passing through the sheet skew correction unit 20, the first shutter member 30 is held in a position (first position) where the contact surface 33a is located upstream of the nip portion N (downward in Figure 3) with respect to the sheet transport direction (downward in Figure 3). 【0031】 When the first shutter member 30 is in the first position shown in Figure 3, the contact surface 33a is inclined such that the angle it makes with the nip tangent L1 (see Figure 8) is acute (90 degrees or less). More specifically, the contact surface 33a is formed such that the angle it makes with the nip tangent L1 is acute from the time the leading edge of the sheet S abuts against the contact surface 33a of the first shutter member 30 until it reaches the nip portion N of the transport roller pair 21. 【0032】 In other words, the contact surface 33a is inclined in a direction that causes the leading edge of the sheet S to move along the contact surface 33a toward the locking portion 33b (main body portion 32) from the moment the conveyed sheet S hits the contact surface 33a until it reaches the nip portion N of the conveying roller pair 21. 【0033】 The locking portion 33b locks the leading edge of the sheet S that abuts against the contact surface 33a, restricting the sheet S so that its leading edge is aligned in a straight line over the entire sheet width direction perpendicular to the conveying direction of the sheet S. Specifically, the locking portion 33b restricts the sheet S so that its leading edge is aligned in a straight line in the sheet width direction from the time the leading edge of the sheet S abuts against the restricting portion 33 until the first shutter member 30 rotates and moves to the nip portion N. 【0034】 Furthermore, the first shutter member 30 is biased by a torsion spring 34 provided on the rotating shaft 22 so that the contact surface 33a is directed towards the upstream side in the sheet transport direction (counterclockwise direction in Figure 3). The configuration of the first shutter member 30 has been described above, and the second shutter member 31 has a similar configuration. 【0035】 The first shutter member 30 and the second shutter member 31 contact the leading edge of the sheet S upstream of the nip portion N of the transport roller pair 21 in the sheet transport direction, locking the sheet S, and then rotate to guide the sheet S to the nip portion N. In other words, the first shutter member 30 and the second shutter member 31 contact the sheet S and lock it before the sheet S is gripped by the nip portion N of the transport roller pair 21, and then rotate to guide the sheet S to the nip portion N. 【0036】 Next, the correction of the sheet S's skew in the sheet skew correction unit 20 will be explained with reference to Figures 3, as well as Figures 4 to 7. Figures 4 to 7 are side cross-sectional views showing the behavior of the sheet S as it passes through the first shutter member 30. The behavior of the sheet S as it passes through the second shutter member 31 is the same as in Figures 4 to 7. The sheet S, transported from the paper cassette 16 to the sheet skew correction unit 20, is guided by guide sections 28a and 28b and transported towards the nip section N of the transport roller pair 21. 【0037】 Figure 4 shows the state in which the leading edge of the sheet S is in contact with the contact surface 33a of the first shutter member 30. As the sheet S is further transported, as shown in Figure 4, the leading edge of the sheet S comes into contact with the contact surface 33a formed on the restricting portion 33 of the first shutter member 30 in the first position. As mentioned above, the contact surface 33a is formed at an acute angle with respect to the nip tangent L1. Therefore, when the leading edge of the sheet S comes into contact with the contact surface 33a, the leading edge of the sheet S moves along the contact surface 33a toward the locking portion 33b. 【0038】 Figure 5 shows the state after the sheet S has been transported a predetermined amount from the state in Figure 4, and the leading edge of the sheet S has moved to the locking portion 33b of the first shutter member 30. The leading edge of the sheet S is locked by the locking portion 33b while pressing against the first shutter member 30 in the sheet transport direction (clockwise direction in Figure 4). The first shutter member 30 is biased by the torsion spring 34 (see Figure 3) in the direction that maintains the first posture (counterclockwise direction in Figure 4). Therefore, the first shutter member 30 does not rotate, and as the sheet S is transported further in the transport direction, a deflection is formed in the sheet S due to the reaction force received from the first shutter member 30. 【0039】 When sheet S is skewed, the leading edge of the preceding sheet S (the leading edge on one side in the width direction of sheet S that will be ahead due to the skew) comes into contact with the contact surface 33a of one of the pair of first shutter members 30. When the leading edge of the preceding sheet S is locked into the locking portion 33b of the first shutter member 30, the leading edge of sheet S comes into contact with the contact surfaces 33a of the second shutter member 31 on one side, the second shutter member 31 on the other side, and the first shutter member 30 on the other side in sequence, and is locked by their respective locking portions 33b. 【0040】 As a result, the entire width of the leading edge of the sheet S follows a uniform straight line so as to press against the locking portions 33b of the pair of first shutter members 30 and the pair of second shutter members 31. In other words, the leading edge of the sheet S becomes parallel to the rotation axis 22, and the skew of the sheet S is corrected. 【0041】 As the sheet S is transported further from the state shown in Figure 5, the stiffness of the sheet S increases the force with which its tip presses against the locking portion 33b. When this pressing force becomes greater than the reaction force (biasing force of the torsion spring 34) received from the first shutter member 30 and the second shutter member 31, the first shutter member 30 and the second shutter member 31, supported by the rotation shaft 22, rotate against the biasing force of the torsion spring 34. At this time, since the tip of the sheet S is pressing against the locking portions 33b of the first shutter member 30 and the second shutter member 31, the sheet S moves while its tip remains in contact with each locking portion 33b. 【0042】 Figure 6 shows the state in which a predetermined amount of sheet S has been conveyed from the state in Figure 5, the first shutter member 30 has rotated and sheet S has passed through the nip portion N of the conveyor roller pair 21. From the state in Figure 5, the first shutter member 30 and the second shutter member 31 rotate, and when the locking portion 33b moves to the side of the nip portion N (to a position where the nip portion N and the locking portion 33b overlap when viewed from the axial direction), the leading edge of sheet S enters the nip portion N and is gripped by the conveyor roller pair 21. When sheet S is gripped by the conveyor roller pair 21, the rotation shaft 22 rotates, causing the drive roller 21a and driven roller 21b to rotate. 【0043】 As the drive roller 21a and driven roller 21b rotate, the sheet S is conveyed while being held in the nip section N, and the locking section 33b is pressed against the leading edge of the conveyed sheet S, causing the first shutter member 30 and the second shutter member 31 to rotate further. As shown in Figure 6, when the regulating sections 33 of the first shutter member 30 and the second shutter member 31 rotate to a position (second position) where they do not overlap the nip tangent L1, the locking between the locking section 33b and the sheet S is released. As a result, the sheet S is conveyed toward the nip section (secondary transfer nip section) between the intermediate transfer belt 8 and the secondary transfer roller 9. 【0044】 Figure 7 shows the state immediately after the sheet S has been conveyed by a predetermined amount from the state in Figure 6, and the rear end of the sheet S has passed the nip portion N of the conveyor roller pair 21. When the rear end of the sheet S passes the nip portion N of the conveyor roller pair 21, the first shutter portion 30 and the second shutter member 31 return to the first position due to the biasing force of the torsion spring 34. 【0045】 Next, the differences between the first shutter section 30 and the second shutter member 31, which are characteristic features of this embodiment, will be explained. Figures 8 and 9 are side cross-sectional views showing the relationship between the locking portion 33b of the first shutter member 30 and the second shutter member 31 and the nip tangent L1 of the transport roller pair 21, respectively. The nip tangent L1 is a straight line that passes through the nip portion N of the transport roller pair 21 and is perpendicular to the straight line L2 that passes through the rotation centers of the drive roller 21a and the driven roller 21b. 【0046】 As shown in Figure 8, the locking portion 33b of the first shutter member 30 is located closer to the center of rotation of the first shutter member 30 than the nip tangent L1 (right side in Figure 8). On the other hand, as shown in Figure 9, the locking portion 33b of the second shutter member 31 is located further from the center of rotation of the second shutter member 31 than the nip tangent L1 (left side in Figure 9). 【0047】 In other words, the locking portion 33b of the second shutter member 31 is formed radially outward compared to the locking portion 33b of the first shutter member 30. Therefore, the force (rotational moment) required for the sheet S to rotate the second shutter member 31 is smaller than the force (rotational moment) required to rotate the first shutter member 30. 【0048】 As a result, the tip of the smaller sheet S, which is less rigid than the larger sheet, can more easily rotate the second shutter member 31, making it easier for the smaller sheet S to slip out of the nip portion N, thus suppressing bending and damage to the smaller sheet S. 【0049】 On the other hand, if the second shutter member 31 rotates easily with a small rotational moment, there is a concern that the sheet S's ability to correct its skew will decrease. However, because a small sheet S has less rigidity, it requires a larger amount of deflection to press against the second shutter member 31, making it easier to correct its skew compared to a large sheet S. 【0050】 Based on the above, the configuration of this embodiment has the effect of expanding the range in which two conflicting requirements—sheet bending and scratch prevention and skew correction capability—are met. Accordingly, the designable range (operation window) of the sheet skew correction unit 20, which corrects skew using the first shutter member 30 and the second shutter member 31, can be expanded compared to the conventional design. 【0051】 Furthermore, by forming the locking portion 33b of the first shutter member 30 radially inward from the nip tangent L1, and the locking portion 33b of the second shutter member 31 radially outward from the nip tangent L1, the radial distance between the locking portion 33b of the first shutter member 30 and the locking portion 33b of the second shutter member 31 can be increased. Consequently, bending and damage to small-sized sheets S can be more effectively suppressed, and the design range of the sheet skew correction unit 20 can be further expanded. 【0052】 In this embodiment, the locking portion 33b of the first shutter member 30 is formed radially inward from the nip tangent L1, and the locking portion 33b of the second shutter member 31 is formed radially outward from the nip tangent L1; however, the embodiment is not limited to this. 【0053】 In other words, the locking portion 33b of the second shutter member 31 only needs to be formed radially outward compared to the locking portion 33b of the first shutter member 30. Both the locking portion 33b of the first shutter member 30 and the locking portion 33b of the second shutter member 31 may be formed radially inward from the nip tangent L1, or both the locking portion 33b of the first shutter member 30 and the locking portion 33b of the second shutter member 31 may be formed radially outward from the nip tangent L1. 【0054】 Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, in the above embodiment, a sheet skew correction unit 20 comprising a pair of first shutter members 30 arranged outside the transport roller pair 21 and a pair of second shutter members 31 arranged between the transport roller pair 21 was described, but the invention is not limited thereto. 【0055】 For example, the sheet may be provided with n pairs (n is an integer of 2 or more) of shutter members arranged symmetrically from the inside to the outside in the sheet width direction, and the m-th pair (m is an integer of 1 or more and n-1 or less) of shutter members from the inside in the sheet width direction may have its locking portion 33b formed radially outward compared to the m+1 pair of shutter members adjacent to it on the outside in the sheet width direction. 【0056】 By configuring the sheet S in this way, even in configurations with three or more pairs of shutter members, the force (rotational moment) required to rotate the shutter member in contact with the sheet S can be reduced as you move from the outside to the inside in the sheet width direction. Therefore, regardless of the size of the sheet S, it is possible to achieve both the ability to correct the skew of the sheet S and the prevention of bending and damage to the sheet S. 【0057】 Furthermore, although the above embodiment described an image forming apparatus 100 using a color printer as an example as shown in Figure 1, the present invention is not limited to color printers and can be applied to various image forming apparatuses equipped with a sheet skew correction unit 20 that corrects the skew of the sheet using a shutter member material, such as color copiers, color multifunction printers, monochrome printers, monochrome copiers, and monochrome multifunction printers. [Industrial applicability] 【0058】 The present invention can be used in a sheet conveying device that conveys a sheet while correcting the sheet's skew using a shutter member, and in an image forming apparatus equipped therewith. By using the present invention, it is possible to provide a sheet conveying device and an image forming apparatus equipped therewith that maintain the skew correction capability of a skew correction mechanism using a shutter member while also expanding the design flexibility. [Explanation of Symbols] 【0059】 3 20. Sheet skew correction unit (sheet transport device) 21 Conveyor roller pair 21a Drive roller 21b Driven roller 22 Rotating shaft (drive roller) 23. Rotating shaft (driven roller) 25 Coil springs 28a, 28b Guide section 30 First shutter member 31. Second shutter component 32 Main body 33 Regulatory Department 33a Contact surface 33b Locking part 100 Image forming apparatus L1 Nip tangent N Nip section

Claims

[Claim 1] A pair of conveying rollers for conveying a sheet, comprising a drive roller and a driven roller that contacts the drive roller with a predetermined pressure to form a nip portion, A main body portion is rotatably supported on the rotation axis of the drive roller and is formed to have approximately the same diameter as the radius of the drive roller, A restricting portion is provided that protrudes radially outward from the outer edge of the main body and contacts the leading edge of the sheet toward the nip portion upstream of the nip portion in the sheet conveying direction, thereby restricting the leading edge of the sheet. It has, The orientation can be changed between a first orientation in which the regulating part can correct the slanting of the sheet, and a second orientation in which the sheet is rotated from the first orientation to guide the sheet to the nip portion. The aforementioned regulatory body, When the shutter member is in the first position, the contact surface against which the leading edge of the sheet abuts, A locking portion is formed at the boundary between the main body and the contact surface, and the leading edge of the sheet is locked into it. A shutter member having, In a sheet transport device equipped with, The shutter member is N pairs (where n is an integer of 2 or more) are arranged symmetrically from the inside outward in the sheet width direction, which is perpendicular to the sheet transport direction. A sheet conveying device characterized in that the m-th pair (where m is an integer between 1 and n-1) of shutter members from the inside in the sheet width direction has its locking portion formed radially outward compared to the m+1 pair of shutter members adjacent to it on the outside in the sheet width direction. [Claim 2] The shutter member is A pair of first shutter members that only contact the sheet whose size in the sheet width direction exceeds a predetermined size, A pair of second shutter members are positioned inside the sheet width direction of the first shutter member and contact the sheet, the size of which in the sheet width direction is less than or equal to a predetermined size, It has, The sheet conveying device according to claim 1, characterized in that the second shutter member has the locking portion provided radially outward compared to the first shutter member. [Claim 3] When the nip tangent is defined as a line perpendicular to the line passing through the nip portion and passing through the rotation centers of the drive roller and the driven roller, The sheet conveying device according to claim 2, characterized in that the locking portion of the first shutter member is provided radially inward from the nip tangent, and the locking portion of the second shutter member is provided radially outward from the nip tangent. [Claim 4] An image forming apparatus comprising a sheet transport device according to any one of claims 1 to 3.

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