JP2005263343A - Sheet transport device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet transport device preventing a sheet from being skewed in the direction disadvantageous to lateral registration correction (the direction where the trailing end of the sheet goes away from a reference plate 24) when the trailing end of the sheet passes through the nip of a clamping and transporting means on the upstream side of a reversing part whereby the lateral registration is efficiently corrected, and an image forming apparatus. <P>SOLUTION: In order to solve the problem, the representative constitution of the invention is as follows. The sheet transport device includes: the reference plate disposed on one side of the sheet transport path and correct the sheet in a predetermined width direction position by regulating the side end of the sheet; a correction transport means disposed in the vicinity of the reference surface to apply the transport force oblique toward the reference surface to the sheet; the clamping transport means disposed on the upstream side of the correction transport means to clamp the sheet; and a guide means for guiding the sheet from the clamping transport means to the paired correction rollers. The guide means is different in the transport distance from the clamping transport means to the correction transport means between both sides in the width direction of the sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus having the same, for example, a printer, a facsimile, a copying machine, and the like, and more particularly to a sheet conveying apparatus suitable for correcting skew of a sheet.

  An image forming apparatus that forms an image on a sheet preferably includes a “lateral registration correcting unit” that corrects a deviation in the width direction of the sheet in order to maintain good recording accuracy of the sheet. In particular, in an apparatus that forms an image on both sides of a sheet, the conveyance path becomes long, so that it is highly necessary to correct a deviation in the width direction that occurs during conveyance in image formation on the first surface. Therefore, conventionally, a configuration in which a lateral registration correction unit is provided in the re-conveying unit before image formation on the second surface is shown.

  Japanese Patent Laid-Open No. 2000-233850 has been proposed as an example of a conventional sheet conveying apparatus provided with a lateral registration correcting means, and this known configuration will be described with reference to FIGS. FIG. 7 is a main cross-sectional view of a laser beam printer as an example of a conventional image forming apparatus, and FIGS. 8 and 9 are flat views of the sheet conveyance path of the sheet re-conveyance unit 103 from the discharge roller 117 to the re-feed roller 120. And it is the figure seen from the top.

  The laser beam printer 101 shown in the figure can form an image on both sides of a sheet as well as an image forming unit 102 for forming an image and a sheet re-conveying unit 103 as a sheet conveying device for reversing the sheet. ing.

  When images are formed on both sides of the sheet P, the sheet P is conveyed to the discharge roller 117 after the image is formed by the image forming unit 102. When the discharge roller 117 rotates in the reverse direction, the sheet P is switched back with the trailing edge of the sheet P being the leading edge, and is continuously sent to the sheet re-conveying unit 103. The sheet re-conveying unit 103 includes, from upstream, a discharge roller 117 as a nipping and conveying unit, a reversing guide 122 that forms a curved conveying path, a lateral registration correcting unit 123 that corrects the width direction position of the conveyed sheet, and a lateral registration correcting unit 123. The re-feed roller 120 is arranged further downstream in the transport direction. The sheet P sent to the sheet re-conveying unit 103 is corrected in the width direction position by the lateral registration correcting unit 123 and then sent again to the image forming unit 102 by the re-feeding roller 120 to perform image formation on the second side. Then, the sheet is discharged from the sheet discharge unit 116 to the outside of the apparatus.

  Here, the configuration and operation of the lateral registration correcting unit 123 in the sheet re-conveying unit 103 will be described with reference to FIG. The lateral registration correction unit 123 includes a reference plate 124 including a reference surface 124a, a lateral registration correction roller 125 and a skew feeding roller 126 that constitute a correction roller pair, and a conveyance lower guide 127. On the downstream side of the lateral registration correcting unit 123, a refeeding unit is provided in which the refeeding roller 120 forms a nip and performs refeeding.

  The reference plate 124 is fixed to the main body of the laser beam printer 101, and includes a lateral registration correction roller 125, a sheet side end guide 124d including a reference surface 124a and a tapered surface 124b, a sheet lower surface guide 124e, and the like. It is a member. The sheet-side end guide 124d has a tapered surface 124b from the intersection 124c on the upstream side of the lateral registration correction roller 125.

  The lateral registration correction roller 125 is held on the reference plate 124 via a bearing (not shown), and sandwiches the sheet in a predetermined region in the width direction. Further, it is arranged so that its rotation axis is perpendicular to the transport direction.

  The skew feeding roller 126 is rotatably held by the reference plate 124 and is urged by the lateral registration correction roller 125 by a spring (not shown) to form a nip. Further, the rotation axis of the oblique feeding roller 126 is arranged so as to have an inclination of about 7 ° toward the reference surface 124a with respect to the rotation axis of the lateral registration correction roller 125. That is, the angle formed between the skew feeding roller 126 and the reference surface 124a is an acute angle on the downstream side, and an oblique transport force (slope feeding force) toward the reference surface 124a is applied to the conveyed sheet.

  The lateral registration correction roller 125 and the oblique feeding roller 126 are arranged on one side in the sheet width direction (closer to the right end as viewed from the front of the apparatus in FIG. 8) together with the reference surface 124a. In this case, the one side is at least the end side from 1/3 of the sheet width.

  Next, the lateral registration correcting operation by the lateral registration correcting unit 123 will be described with reference to FIG. The sheet P1 conveyed to the lateral registration correction unit 123 by the discharge roller 117 eventually reaches the lateral registration correction roller 125 and the skew feeding roller 126. In a state where the rear end of the sheet P1 is nipped by the nip of the discharge roller 117, only the front end of the sheet P2 approaches the reference surface 124a by receiving the oblique feeding force F1 of the oblique feeding roller 126 (FIG. 9A).

  Thereafter, when the rear end of the sheet P2 passes through the nip of the discharge roller 117, the sheet P2 receives a sliding resistance force F2 of the lower conveyance guide 127, and a rotational force F3 is generated so that the rear end of the sheet P2 approaches the tapered surface 124b side. Since the sheet P2 is tilted by the rotational force F3, the sheet P3 becomes closer to the reference plane 124a (FIG. 9B).

  The sheet P3 abuts on the intersection 124c between the reference surface 124a and the tapered surface 124b, and the reaction force F4 generates a reverse rotational force F5 that brings the front end of the sheet P3 closer to the reference surface 124a. The sheet P4 is positioned along the reference surface 124a. (FIG. 9C).

  As described above, the sheet conveying apparatus having the lateral registration correcting means using the pair of lateral registration correcting rollers as described above can perform lateral registration correction relatively efficiently.

JP 2000-233850 A

  However, the sheet conveying apparatus including the lateral registration correcting unit that performs lateral registration correction by rotating the sheet by the conveying force of the pair of conveying rollers provided in the predetermined region in the width direction as described in the conventional example is also described below. There was a problem like this.

  In the conventional example, as shown in FIG. 10A, the discharge roller 117 and the lateral registration correction roller 125 are disposed close to each other, and the sheet is temporarily sandwiched between both rollers and conveyed. In general, the sheet conveyance speeds of the discharge roller 117 and the lateral registration correction roller 125 are set to be constant or slower than the lateral registration correction roller 125. This is because the lateral registration correction roller 125 becomes faster, and when the sheet P is pulled in the conveyance direction between the two rollers, the upper surface of the sheet is rubbed against the upper reversing guide 128 (see FIG. 7) in the reversing portion. This is to smudge the image.

  However, when the conveyance speed of the discharge roller 117 and the lateral registration correction roller 125 is constant speed or a slack system (when the sheet is nipped and conveyed by two conveyance means at the same time, the downstream conveyance means is slower), When the trailing edge of the sheet P passes through the nip of the discharge roller 117, the sheet P curved at the reversing part tends to be straightened by its own waist, so that the leading edge of the sheet P is pushed forward (downstream in the conveying direction). . At this time, the sheet P is nipped at the reference plate side end portion by the lateral registration correction roller 125, but the non-reference plate side end portion is free. Therefore, as shown in FIG. A rotational force F6 is received in the direction in which the side tip comes out.

  In other words, the leading edge of the sheet P approaches the reference surface 124a greatly, and the trailing edge is greatly separated from the reference surface 124a. By tilting in this way, it takes time to correct the lateral registration, which is disadvantageous in terms of performance. In order to avoid this influence, it is conceivable to set the interval between the discharge roller 117 and the lateral registration correction roller 125 to be equal to or longer than the sheet length. This will increase the size of the device.

  Further, such a behavior of the sheet P is particularly remarkable in the case of a stiff sheet such as a thick paper, and there is a difficulty that a difference in lateral registration correction ability is caused depending on the thickness of the sheet.

  The present invention has been made in view of the above-described problems, and the object of the present invention is firstly disadvantageous in correcting lateral registration when the rear end of the sheet passes through the nip of the nipping and conveying means upstream of the reversing unit. It is an object of the present invention to provide a sheet conveying apparatus and an image forming apparatus that can prevent a sheet from being inclined in a proper direction (a direction in which the rear end of the sheet separates from the reference plate 24) and can perform lateral registration correction efficiently. Secondly, the first object is achieved regardless of the thickness of the sheet.

  In order to solve the above-described problems, a typical configuration of the present invention is a reference having a reference surface that is disposed on one side of a sheet conveyance path and regulates a sheet to a predetermined width direction position by regulating a sheet side end. A correction conveying means that is disposed in the vicinity of the reference plane and that imparts an oblique conveying force toward the reference plane to the sheet; and a nipping and conveying means that is disposed upstream of the correction conveying means and sandwiches and conveys the sheet; In the sheet conveying apparatus including a guide unit that guides the sheet from the nipping / conveying unit to the correction roller pair, the guide unit is configured such that a conveyance path length from the nipping / conveying unit to the correction conveying unit is a sheet width. It is characterized by being different on both sides in the direction.

  According to the present invention, the guide means is configured such that the conveyance path length from the nipping and conveying means to the correction conveying means is different on both sides in the sheet width direction, so that the rear end of the sheet is separated from the nipping and conveying means. In addition, it is possible to absorb the behavior of pushing the leading edge of the sheet downstream in the conveyance direction due to the difference in the conveyance path length, and to prevent the sheet from being inclined in a direction that is disadvantageous for the lateral registration correction, and to efficiently perform the lateral registration correction. It is possible to provide a sheet conveying apparatus that can perform the above operation. Further, since the lateral registration correction can be performed efficiently with a short conveyance path, the apparatus can be downsized and the production cost can be reduced.

[First embodiment]
A first embodiment of a sheet conveying apparatus and an image forming apparatus according to the present invention will be described. Specific configurations and dimensions of members and arrangements shown below are examples for facilitating understanding of the invention, and the present invention is not limited thereto.

  First, the overall configuration of the image forming apparatus will be described with reference to FIG. FIG. 1 shows a laser beam printer capable of double-sided recording as an example of an image forming apparatus.

  The laser beam printer main body 1 includes an image forming unit 2 that forms an image on both sides of a sheet, and a sheet re-conveying unit 3 as an example of a sheet conveying device that performs lateral registration correction. The plurality of sheets P stacked on the cassette 4 are picked up by the feeding roller 5 and separated and fed one by one by the feeding unit 6. The photosensitive drum 7 and process means (charging device, developing device, and cleaning device) that act on the photosensitive drum 7 are integrally formed as a process cartridge 8 and are configured to be detachable from the printer main body 1. The toner image formed on the photosensitive drum 7 is transferred onto the sheet P by the transfer roller 9 and fixed semi-permanently by the fixing unit 10. On the downstream side of the fixing unit 10, a post-fixing roller 13, a first roller 14, a discharge guide 15, a sheet discharge unit 16, a discharge roller pair 17 including a pair of rollers and rollers, and a discharge stacking unit 19 are provided.

  The controller board 11 controls the printer body 1. When a print signal is received from a computer (not shown) to which the image forming unit 2 is connected, the controller board 11 performs an image forming process to create an image signal. The laser scanner unit 12 irradiates the photosensitive drum 7 with laser light corresponding to the image signal created by the controller board 11 to form a latent image.

  When the controller board 11 receives a single-sided image formation signal, the sheet P is nipped and conveyed by the discharge roller pair 17 and discharged to the discharge stacking unit 19. Here, the single-sided image formation signal is a signal sent to the controller board 11 from a personal computer (not shown) as in the case of the print signal and the image signal.

  When the controller board 11 receives a double-sided image formation signal, the discharge roller pair 17 rotates in the reverse direction after the sheet trailing edge passes through the nip of the first roller 14 facing the post-fixing roller 13. As a result, the sheet P is switched back, passes through the substantially vertical reversing path 18, and is continuously sent to the sheet re-conveying unit 3. The discharge roller pair 17 is driven by a motor (not shown) independent of the other rollers.

  Next, the configuration and operation of the sheet re-conveying unit 3 and the lateral registration correcting unit 23 will be described with reference to FIGS. FIG. 2 is a plan view of the sheet conveyance path of the sheet re-conveyance unit 3 from the discharge roller pair 17 to the re-feed roller 20 as viewed from above, and FIG. 3 is a perspective view illustrating the lateral registration correction unit. 4 is a perspective view for explaining the lateral registration correcting portion and its operation, and FIG. 5 is a top view for explaining the operation by developing the lateral registration correcting portion on a plane.

  As shown in FIG. 1, the sheet re-conveying unit 3 is configured around a conveying path starting from the discharge roller pair 17 and reaching the junction 21 with the conveying path from the cassette 4. The sheet P after the sheet reversal is nipped and conveyed by a nip formed by the discharge roller pair 17. In this embodiment, the same conveyance path is used for the first conveyance path and the second conveyance path from the post-fixing roller 13 to the nip of the discharge roller pair 17. Four or more discharge roller pairs 17 are arranged in the sheet width direction in order to suppress the rotational movement of the sheet P during conveyance.

  As shown in FIG. 1, the sheet re-conveying unit 3 includes a reversing guide 22 for guiding from a substantially vertical reversing path 18 to a substantially horizontal lateral registration correcting unit 23, a lateral registration correcting unit 23 serving as a lateral registration correcting unit, A reference plate 24, a lateral registration correction roller 25 and a skew feeding roller 26 constituting a correction conveying means, a conveying lower guide 27, an inversion upper guide 28, and a refeeding roller 20 as a refeeding means are provided. The lateral registration correction unit 23 includes a reference plate 24 including a reference surface 24a, a pair of conveyance rollers including a lateral registration correction roller 25 and a skew feeding roller 26 as a lateral registration correction roller, and a conveyance lower guide 27. It is a configuration. The lateral registration correction unit 23 is provided for the purpose of correcting the position of the sheet P, which has been shifted during conveyance, to a predetermined position in the width direction along the reference surface 24a before forming the second image.

  As shown in FIG. 2, the reference plate 24 includes a reference surface 24a, a tapered surface 24b, a sheet-side end guide 24d composed of an intersection 24c, and a sheet lower surface guide 24e. The sheet side end guide 24d has a tapered surface 24b from the intersection 24c on the upstream side of the lateral registration correction roller 25. The reference surface 24a is a surface that coincides with the edge of one side of the maximum width sheet conveyed to the sheet reconveying unit 3 (right side as viewed from the front of the apparatus in this embodiment).

  The lateral registration correction roller 25 is held by the reference plate 24 via a bearing (not shown), and clamps the sheet in a predetermined region in the width direction. Further, it is arranged so that its rotation axis is perpendicular to the transport direction. The oblique feeding roller 26 is rotatably held by the reference plate 24 and is urged by a lateral registration correction roller 25 by a spring (not shown) to form a nip. Further, the rotation axis of the oblique feeding roller 26 is disposed so as to have an inclination of about 7 ° toward the reference surface 24a with respect to the rotation axis of the lateral registration correction roller 25. That is, the angle formed between the skew feeding roller 26 and the reference surface 24a is an acute angle on the downstream side, and an oblique transport force (slope feeding force) toward the reference surface 24a is applied to the conveyed sheet. The lateral registration correction roller 25 and the skew feeding roller 26 are arranged on one side in the sheet width direction (in FIG. 2, near the right end as viewed from the front of the apparatus) together with the reference plate 24. In this case, one side is at least the end side from the sheet width 1/3.

  As shown in FIG. 3, the reversing guide 22 has a continuous cross-sectional shape with different radii on the left and right sides in the sheet width direction, the reference plate side reversing guide 22a on the side where the reference plate 24 is arranged, and the non-reference plate reversing side on the other side. It will be called a guide 22b. The reference plate side reversing guide 22a has a large radius of curvature of approximately R90 mm, and the non-reference plate reversing guide 22b has a small radius of curvature of approximately R60 mm. The reversing guide 22 between the two radii is smoothly connected with a continuous cross-sectional shape in which the curvature radius changes. For this reason, the length of the conveyance path from the discharge roller pair 17 to the lateral registration correction roller 25 differs on the left and right in the sheet width direction. That is, the conveyance path is short on the reference plate side having a large curvature radius, and the conveyance path is long on the non-reference plate side having a small curvature radius. Therefore, the arrival time to the horizontal registration correction roller 25 is set so that the reference plate 22 side is earlier.

  The lateral registration correction operation in the case where the sheet P is conveyed to the lateral registration correction unit 23 in a state of being separated from the reference surface 24a in the lateral registration correction unit 23 having the above configuration will be described with reference to FIG.

  When the sheet is guided to the reversing guide 22 from the substantially vertical reversing path 18 provided at the rear of the printer body 1 by the discharge roller pair 17 and conveyed to the lateral registration correcting unit 23 (see FIG. 1), the leading edge of the sheet P1 The part of the reference plate side reversing guide 22a side having a larger radius advances first, and the non-reference plate side reversing guide 22b side having a smaller radius is conveyed with a delay.

  Eventually, as shown in FIG. 4A, the leading edge of the sheet P1 reaches the nip between the lateral registration correction roller 25 and the skew feeding roller 26. Then, as shown in FIG. 5A, in a state where the rear end of the sheet P1 is sandwiched between the nips of the discharge roller pair 17, only the front end of the sheet P2 receives the oblique feeding force F1 of the oblique feeding roller 26 on the reference surface 24a. Approaching.

  Thereafter, when the rear end of the sheet P2 passes through the nip of the discharge roller pair 17, the sheet P1 curved at the reversing guide 22 portion tends to be straightened by its own waist, and as shown in FIG. The tip of the shaft receives a rotational force F6 in the direction pushed forward (downstream in the transport direction). At this time, the reference plate side end portion of the sheet P1 is sandwiched between the lateral registration correction roller 25 and the oblique feeding roller 26, but the non-reference plate side end portion of the sheet P1 is not restrained. The tip of the non-reference plate side will rotate in the direction to come forward.

  However, in this configuration, since the conveyance path on the reference plate side is short and the conveyance path on the non-reference plate side is long, the sheet is preceded on the reference plate side, and is inclined (skewed) in advance in a direction away from the reference plate 24. doing. Therefore, even if the leading edge of the sheet is pushed out when the trailing edge of the sheet is removed from the pair of discharge rollers 17, the rotational force F6 is alleviated due to the difference in the length of the conveyance path, and the rotational force F6 is one. Even if it is rotated by, it will act to return the inclination given in advance.

  Thereafter, upon receiving the sliding resistance force F2 of the lower conveyance guide 27, a rotational force F3 is generated on the sheet P2 so as to bring the rear end closer to the reference surface 24a side. Since the sheet P2 is tilted by the rotational force F3, the sheet P3 comes closer to the reference plane 24a as shown in FIG. 5B.

  The sheet P3 abuts on the intersection 24c between the reference surface 24a and the tapered surface 24b, and the reaction force F4 generates a reverse rotational force F5 that brings the front end of the sheet P3 closer to the reference surface 24a side, as shown in FIG. The sheet P4 is aligned at a position along the reference surface 24a.

  As described above, in the image forming apparatus provided with the sheet conveying device having the lateral registration correcting unit using the pair of lateral registration correcting rollers on the one-side basis as described above, the conveyance between the nipping conveying unit and the correction roller pair. By providing a difference in the length of the path, it is possible to control the behavior when the leading edge of the sheet is pushed out. The leading edge of the non-reference plate protrudes and the sheet is disadvantageous for lateral registration correction (the trailing edge of the sheet is the reference plate). It is possible to prevent lateral tilting (in a direction away from 24) and perform lateral registration correction efficiently. In addition, since the lateral registration can be corrected efficiently with a short conveyance path, a sheet conveyance apparatus that is downsized and reduced in cost can be provided. In particular, the resistance of the thick paper is large, and the tip of the non-reference side tends to protrude, but this can be sufficiently suppressed, and the lateral registration can be reliably corrected even for the thick paper.

  In addition, since the reversing guide 22 has a continuous cross-sectional shape in which the radius of curvature changes in the sheet width direction, the sheet can be conveyed smoothly. Further, by setting the bending radius of curvature of the guide means between R60 mm and R90 mm, the sliding resistance by the conveying member does not increase, and lateral registration correction by oblique feeding can be performed without any trouble.

[Second Example]
A second embodiment of the sheet conveying apparatus and the image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 6 is a perspective view for explaining the lateral registration correcting portion and its operation according to the present embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  In the first embodiment, the length of the conveyance path is different on both sides in the sheet width direction by making the shapes of the reference plate side inversion guide 22a and the non-reference plate side inversion guide 22b of the inversion guide 22 different. Explained. In this case, the conveyance path is a space sandwiched between a reversing guide 22 that defines the lower side of the sheet and a reversing upper guide 28 that defines the upper side of the sheet. Is formed in a shape that follows the reversing guide 22, which means that the conveying path is formed as a space whose upper and lower surfaces are parallel.

  In contrast, in this embodiment, the reversing guide 22 (outer guide means) positioned outside the bending in the transport direction has a general shape, that is, a cross-sectional shape orthogonal to the bending in the transport direction. Only the upper reversing guide 28 (inner guide means) positioned inside the bending in the conveying direction is configured such that the conveying path length from the discharge roller pair 17 to the lateral registration correction roller 25 is different on both sides in the sheet width direction. It is a thing.

  As shown in FIG. 6, the vicinity of the reversing guide 22 of the reversing upper guide 28 is located inside the bending of the conveyance path in the reversing guide 22. The reversing upper guide 28 has a continuous cross-sectional shape with different curvature radii on the left and right sides in the sheet width direction in the vicinity of the bending position. It will be referred to as the upper guide 28b. The reference plate side inversion upper guide 28a has a large radius of curvature, and the non-reference plate side inversion upper guide 28b has a small radius of curvature. The reversing upper guide 28 between the two radii is smoothly connected with a continuous cross-sectional shape in which the radius of curvature changes.

  For this reason, the length of the conveyance path from the discharge roller pair 17 to the lateral registration correction roller 25 is different on the left and right. That is, the conveyance path is short on the reference plate 22 side having a large curvature radius, and the conveyance path is long on the non-reference plate side having a small curvature radius. Therefore, the arrival time to the lateral registration correction roller 25 is set so that the reference plate 24 side is earlier. Here, the length of the conveyance path is different only on the reversing upper guide 28 side on the front and back surfaces of the sheet, and the conveyance path is the same on the reversing guide 22 side. In order to be straightened by its own waist, it is conveyed following the guide means inside the bend, so it is sufficient to change the shape of only the inner guide means.

  Next, the lateral registration correction operation in the case where the sheet P is conveyed to the lateral registration correction unit 23 in a state of being separated from the reference surface 24a in the lateral registration correction unit 23 having the above configuration will be described with reference to FIG. .

  When the sheet is guided to the reversing guide 22 from the substantially vertical reversing path 18 provided at the rear of the printer body 1 by the discharge roller pair 17 and conveyed to the lateral registration correcting unit 23 (see FIG. 1), the leading edge of the sheet P1 The portion of the reference plate side reversing upper guide 28a having a larger radius advances first, and the non-reference plate side reversing upper guide 28b having a smaller radius is conveyed with a delay.

  Eventually, as shown in FIG. 6A, the leading edge of the sheet P1 reaches the nip between the lateral registration correction roller 25 and the skew feeding roller 26. Then, as shown in FIG. 5A, in a state where the rear end of the sheet P1 is sandwiched between the nips of the discharge roller pair 17, only the front end of the sheet P2 receives the oblique feeding force F1 of the oblique feeding roller 26 on the reference surface 24a. Approaching.

  Thereafter, when the rear end of the sheet P2 passes through the nip of the discharge roller pair 17, the sheet P1 curved between the reversing guide 22 and the reversing upper guide 28 tends to be straightened by its own waist. As shown, the leading edge of the sheet P1 receives a rotational force F6 in the direction pushed forward (downstream in the transport direction). At this time, the reference plate side end of the sheet P1 is nipped only by the lateral registration correction roller 25, but the non-reference plate side end of the sheet P1 is not constrained. The side tip rotates in the forward direction.

  However, in this configuration, since the conveyance path on the reference plate side is short and the conveyance path on the non-reference plate side is long, the sheet is preceded on the reference plate side, and is inclined in advance in a direction away from the reference plate 24 (skew). doing. Therefore, even if the leading edge of the sheet is pushed out when the trailing edge of the sheet is removed from the pair of discharge rollers 17, the rotational force F6 is alleviated due to the difference in the length of the conveyance path, and the rotational force F6 is one. Even if it is rotated by this, it acts to return the inclination given in advance.

  Thereafter, upon receiving the sliding resistance force F2 of the lower conveyance guide 27, a rotational force F3 is generated on the sheet P2 so as to bring the rear end closer to the reference surface 24a side. Since the sheet P2 is tilted by the rotational force F3, the sheet P3 comes closer to the reference plane 24a as shown in FIG. 5B.

  The sheet P3 abuts on the intersection 24c between the reference surface 24a and the tapered surface 24b, and the reaction force F4 generates a reverse rotational force F5 that brings the front end of the sheet P3 closer to the reference surface 24a side, as shown in FIG. The sheet P4 is aligned at a position along the reference surface 24a.

  As described above, the sheet re-conveying unit 3 is configured such that the reference plate side conveying path of the inner guide unit is shortened, and the above-described one-side reference is provided with a lateral registration correcting unit using a pair of lateral registration correcting rollers. The lateral registration can be efficiently corrected by the image forming apparatus provided with the sheet conveying apparatus.

  In the first and second embodiments, the bent portions of the reversing guide 22 and the reversing upper guide 28 are provided with arc portions, and it has been described that the radius of curvature is changed. However, the present invention is not limited to this, and it is only necessary that the conveying path lengths are different in the sheet width direction. For example, the cross section may be an elliptical arc, or the bending may be constituted by a plurality of driven rollers.

  With the configuration as described above, in the image forming apparatus including the sheet conveying apparatus configured to include the lateral registration correcting unit using the pair of lateral registration correcting rollers on one side basis, as in the first embodiment, the nipping and conveying unit and the correction are performed. By providing a difference in the length of the conveyance path between the pair of rollers, it is possible to control the behavior when the leading edge of the sheet is pushed out, and the leading edge of the non-reference plate side protrudes so that the sheet is disadvantageous for lateral registration correction ( It is possible to prevent the rear end of the sheet from being inclined in a direction away from the reference plate 24, and to perform lateral registration correction efficiently. In particular, the resistance of the thick paper is large, and the tip of the non-reference side tends to protrude, but this can be sufficiently suppressed, and the lateral registration can be reliably corrected even for the thick paper.

  In addition, since the lateral registration can be corrected efficiently with a short conveyance path, a sheet conveyance apparatus that is downsized and reduced in cost can be provided. As a result, an image forming apparatus equipped with such a sheet conveying apparatus can reliably perform lateral registration correction, has good recording accuracy, can be downsized, and can reduce production costs. In particular, in an apparatus that forms an image on both sides of a sheet, since the conveyance path becomes long, it is highly necessary to provide a lateral registration correction unit in the reconveying unit. Therefore, the sheet conveying apparatus is provided in the reconveying unit. Is preferred.

  The present invention can be used as a sheet conveying device of an image forming apparatus including a lateral registration correcting unit.

This is a laser beam printer capable of duplex recording as an example of an image forming apparatus. It is a plane development view of the sheet conveyance path of the sheet re-conveyance unit. It is a perspective view explaining a lateral registration correction part. It is a perspective view explaining a lateral registration correction part and its operation. It is a top view explaining the effect | action which expand | deploy a horizontal registration correction | amendment part planarly. It is a perspective view explaining the horizontal registration correction | amendment part which concerns on a 2nd Example, and its effect | action. FIG. 10 is a main cross-sectional view of an image forming apparatus according to a conventional example. It is a plane development view of the sheet conveyance path of the sheet re-conveyance unit according to the conventional example. It is a plane development view of the sheet conveyance path of the sheet re-conveyance unit according to the conventional example. It is a perspective view explaining the horizontal registration correction | amendment part which concerns on a prior art example, and its effect | action.

Explanation of symbols

P ... Sheet 1 ... Printer body 2 ... Image forming unit 3 ... Sheet re-conveying unit 4 ... Cassette 5 ... Feeding roller 6 ... Feeding unit 7 ... Photoconductor drum 8 ... Process cartridge 9 ... Transfer roller
10… Fusing unit
11… Controller board
12… Laser scanner unit
13… Roller after fixing
14… first roller
15… discharge guide
16 ... Sheet discharge section
17… discharge roller pair
18… Reverse path
19… discharge loading section
20… Refeed roller
21… Confluence
22… Reversal guide
22a: Reference plate side reversing guide
22b ... Non-reference plate side reversing guide
23… Horizontal registration correction part
24… Reference plate
24a ... Reference plane
24b ... Tapered surface
24c ... Intersection
24d ... Seat side edge guide
24e ... Seat bottom guide
25… Horizontal registration correction roller
26… Inclined roller
27… Conveying lower guide
28… Reverse upper guide
28a ... Reference plate side reversing upper guide
28b ... Non-reference plate side reversing upper guide
101 ... Laser beam printer
102 ... Image forming section
103 ... Sheet re-conveying section
116… Sheet discharge section
117… discharge roller
120… Refeed roller
122… Reversal guide
123… Horizontal registration correction part
124… Reference plate
124a ... Reference plane
124b ... Tapered surface
124c… Intersection
124d ... Sheet side edge guide
124e ... Seat bottom guide
125… Horizontal registration correction roller
126 ... Slope feeding roller
127… Conveying lower guide
128… Inversion upper guide

Claims (8)

A reference plate that is disposed on one side of the sheet conveyance path and has a reference surface that regulates the sheet-side end portion and corrects the sheet to a predetermined width direction position;
Corrective conveying means that is disposed near the reference surface and applies an oblique conveying force toward the reference surface to the sheet;
A nipping and conveying unit disposed on the upstream side of the correction conveying unit and nipping and conveying the sheet; and
In a sheet conveying apparatus comprising guide means for guiding a sheet from the sandwiching conveying means to the correction conveying means,
The sheet conveying apparatus, wherein the guide unit is configured such that a conveyance path length from the holding conveyance unit to the correction conveyance unit is different on both sides in the sheet width direction. 2. The sheet conveying apparatus according to claim 1, wherein the conveying path length is set so that the side on which the reference plate is arranged is short and the other side is long in the sheet width direction. The guide means has a sectional shape in which the radius of curvature continuously changes partially in the sheet width direction,
The sheet conveying apparatus according to claim 1, wherein the radius of curvature continuously changes in the sheet width direction. 4. A sheet conveying apparatus according to claim 3, wherein the radius of curvature of the guide means is set between R60 mm and R90 mm. The guide means forms a conveyance path bent in the sheet conveyance direction, and includes outer guide means arranged outside the bend,
The conveyance path defined by the outer guide means is configured such that the conveyance path length from the nipping conveyance means to the correction conveyance means is different on both sides in the sheet width direction. Item 5. The sheet conveying apparatus according to any one of Items4. The guide means forms a conveyance path bent in the sheet conveyance direction, and includes an outer guide means arranged outside the bend, and an inner guide means arranged inside the bend,
The conveyance path defined by the inner guide means is configured such that the conveyance path length from the clamping conveyance means to the correction conveyance means is different on both sides in the sheet width direction. Item 5. The sheet conveying apparatus according to any one of Items4. A sheet conveying device according to any one of claims 1 to 6,
An image forming apparatus comprising: an image forming unit that forms an image on a sheet. In an image forming apparatus that forms an image on both sides of a sheet,
The image forming apparatus according to claim 7, wherein the sheet conveying device is provided in a reconveying unit that conveys a sheet on which an image is formed on the first surface to the image forming unit again.

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