Sheet conveying device and image forming apparatus

Abstract

To adjust a sheet conveyed along a sheet conveying path to a proper position on the sheet conveying path without applying a load to the sheet.SOLUTION: A sheet conveying device 4 includes a sheet detecting part 10 and a conveying position adjusting mechanism 50. The conveying position adjusting mechanism 50 is arranged downstream in a sheet conveying direction with respect to the sheet detecting part 10 on a sheet conveying path 41, has an adjusting roller pair 51, and performs skew correction and misalignment correction of a sheet S while conveying the sheet S. The sheet conveying path 41 comprises: a first conveying roller pair 42 arranged upstream in the sheet conveying direction with respect to the conveying position adjusting mechanism 50; and a curved part 44 arranged between the adjusting roller pair 51 and the first conveying roller pair 42, and curved in an S shape so as to alternately protrude in front and back directions of the sheet S from different positions in the sheet conveying direction. The adjusting roller pair 51 holds and conveys the sheet S together with the first conveying roller pair 42 .SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying device and an image forming apparatus. [Background technology]

[0002] There is known an image forming apparatus that performs skew correction to correct the inclination of a sheet conveyed along a sheet conveying path with respect to the sheet conveying direction, and positional deviation correction to correct the positional deviation of the sheet in the sheet width direction perpendicular to the sheet conveying direction. An example of such an image forming apparatus is disclosed in Patent Document 1.

[0003] The conventional image forming apparatus disclosed in Patent Document 1 includes a clamping roller that conveys a sheet along a predetermined conveyance path, an upstream detection unit and a downstream detection unit that detect the amount of misalignment of the sheet upstream and downstream of the clamping roller, respectively, and a roller movement mechanism that moves the clamping roller to correct the amount of misalignment of the sheet. A control unit of the image forming apparatus controls the roller movement mechanism based on the amount of upstream misalignment and the amount of downstream misalignment of the sheet. This improves the accuracy of correcting the misalignment of the sheet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-95466 Summary of the Invention [Problem to be solved by the invention]

[0005] When a sheet being conveyed along a sheet conveying path is adjusted to an appropriate position on the sheet conveying path, tension, bending, and twisting occur in the sheet between two pairs of conveying rollers that sandwich and hold the sheet at the upstream and downstream portions of the sheet conveying direction. To eliminate this tension, bending, and twisting, it is necessary to create a deflection in the sheet between these two pairs of conveying rollers aligned along the sheet conveying direction. For this reason, it is preferable to provide a curved portion in the sheet conveying path that protrudes in the direction of the front and back surfaces of the sheet.

[0006] However, in the conventional technology, the conveyance path between the clamping roller and the conveyance roller upstream of the clamping roller does not have a curved portion. This means that when adjusting the position of the sheet, it is not possible to form a sufficient deflection in the sheet, and the tension, bending, and twisting of the sheet cannot be eliminated. As a result, a large load is applied to the sheet, and there is a risk of the sheet being damaged. Furthermore, when the conveyance path has only one curved portion, it is sometimes not possible to sufficiently eliminate the tension, bending, and twisting of the sheet.

[0007] The present invention has been made in consideration of the above points, and aims to provide a sheet conveying device and an image forming device that can adjust a sheet being conveyed along a sheet conveying path to an appropriate position on the sheet conveying path without placing a load on the sheet. [Means for solving the problem]

[0008] In order to solve the above problems, the sheet conveying device of the present invention includes a sheet detection unit and a conveying position adjustment mechanism. The sheet detection unit is disposed on the sheet conveying path and detects the amount of skew of the conveyed sheet with respect to the sheet conveying direction and the amount of positional deviation of the sheet in the sheet width direction perpendicular to the sheet conveying direction. The conveying position adjustment mechanism is disposed on the sheet conveying path downstream of the sheet detection unit in the sheet conveying direction and performs skew correction to correct the skew of the sheet with respect to the sheet conveying direction and positional deviation of the sheet in the sheet width direction based on the detection result of the sheet detection unit while conveying the sheet. The conveying position adjustment mechanism includes an adjustment roller pair, a skew correction motor, and a positional deviation correction motor. The adjustment roller pair nip and convey the sheet. The skew correction motor tilts the adjustment roller pair with respect to the sheet conveying direction. The positional deviation correction motor moves the adjustment roller pair in the sheet width direction. The sheet transport path includes a first transport roller pair disposed upstream of the transport position adjustment mechanism in the sheet transport direction, and curved portions disposed between the adjustment roller pair and the first transport roller pair, and curved in an S shape so as to alternately protrude toward the front and back surfaces of the sheet from different positions in the sheet transport direction. The adjustment roller pair, together with the first transport roller pair, hold and transport the sheet. [Effects of the Invention]

[0009] According to the configuration of the present invention, when the transport position adjustment mechanism is operated to perform skew correction and misalignment correction, the sheet is held and transported by the adjustment roller pair and the first transport roller pair. As a result, the sheet held by the adjustment roller pair and the first transport roller pair is bent into an S-shape when viewed in the sheet width direction. By bending and bending the sheet so that it protrudes in two directions, tension, bending, and twisting can be sufficiently eliminated. Therefore, when a sheet transported along the sheet transport path is adjusted to an appropriate position on the sheet transport path, the adjustment can be made without applying a load to the sheet. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional front view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing a schematic configuration of the image forming apparatus of FIG. 1. [Figure 3] 2 is a side view of a conveying position adjusting mechanism of the image forming apparatus of FIG. 1. FIG. [Figure 4] FIG. 4 is a bottom view of the transfer position adjustment mechanism of FIG. 3. [Figure 5] 4 is a schematic side view showing a first stage of progress of skew correction and position deviation correction by the transfer position adjustment mechanism of FIG. 3. FIG. [Figure 6] 4 is a schematic side view showing a second stage of the progress of skew correction and position deviation correction by the transfer position adjustment mechanism of FIG. 3. FIG. [Figure 7] 4 is a schematic side view showing a third stage of the progress of skew correction and position deviation correction by the transfer position adjustment mechanism of FIG. 3. FIG. [Figure 8] 4 is a schematic side view showing a fourth stage of the progress of skew correction and position deviation correction by the transfer position adjustment mechanism of FIG. 3. FIG. [Figure 9] 2 is a schematic front view of a curved portion of a sheet transport path of the image forming apparatus of FIG. 1. [Figure 10] 10 is a schematic front view of a curved portion of the sheet transport path in FIG. 9, illustrating a state when a transport position adjustment mechanism is operated. FIG. [Figure 11] FIG. 10 is a schematic front view of a curved portion of a modified sheet transport path. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following.

[0012] Fig. 1 is a schematic cross-sectional front view showing the configuration of an image forming apparatus 1 according to an embodiment. Fig. 2 is a block diagram showing the schematic configuration of the image forming apparatus 1 shown in Fig. 1. An example of the image forming apparatus 1 according to this embodiment is a tandem color printer that transfers a toner image onto a sheet S using an intermediate transfer belt 31. The image forming apparatus 1 may be a so-called multifunction peripheral that has functions such as printing, scanning (image reading), and facsimile transmission.

[0013] As shown in Figures 1 and 2, the image forming apparatus 1 includes a sheet supply unit 3, a sheet conveying device 4, an exposure unit 5, an image forming unit 20, a transfer unit 30, a fixing unit 6, a sheet discharge unit 7, a control unit 8, and a memory unit 9, which are provided in its main body 2.

[0014] The sheet supply unit 3 stores multiple sheets S and separates and sends out the sheets S one by one during printing. The sheet transport device 4 transports the sheets S sent out from the sheet supply unit 3 to the secondary transfer unit 33 and the fixing unit 6, and further includes a sheet transport path 41 that discharges the fixed sheets S from a sheet discharge opening 4a to a sheet discharge unit 7. The exposure unit 5 irradiates the image forming unit 20 with laser light controlled based on image data.

[0015] The image forming units 20 are disposed below the intermediate transfer belt 31. The image forming units 20 include an image forming unit 20Y for yellow, an image forming unit 20M for magenta, an image forming unit 20C for cyan, and an image forming unit 20B for black. These four image forming units 20 have the same basic configuration. Therefore, in the following description, the identification symbols "Y," "M," "C," and "B" representing each color may be omitted unless otherwise specified.

[0016] The image forming unit 20 includes a photosensitive drum (image carrier) 21 that is supported so as to be rotatable in a predetermined direction (clockwise in FIG. 1). The photosensitive drum 21 is disposed with its rotation axis horizontal. The image forming unit 20 further includes a charging unit, a developing unit, and a drum cleaning unit that are disposed around the photosensitive drum 21 along its rotation direction. A primary transfer unit 32 is disposed between the developing unit and the drum cleaning unit.

[0017] The photosensitive drum 21 has a photosensitive layer on its outer circumferential surface. The charging unit charges the outer circumferential surface of the photosensitive drum 21 to a predetermined potential. The exposure unit 5 exposes the outer circumferential surface of the photosensitive drum 21 charged by the charging unit to light, forming an electrostatic latent image of the original image on the outer circumferential surface of the photosensitive drum 21. The developing unit develops this electrostatic latent image by attaching toner to form a toner image. Each of the four image forming units 20 forms a toner image of a different color. The drum cleaning unit removes and cleans toner and other substances remaining on the outer circumferential surface of the photosensitive drum 21 after the toner image has been primarily transferred to the outer circumferential surface of the intermediate transfer belt 31.

[0018] The transfer unit 30 includes an intermediate transfer belt 31, primary transfer units 32Y, 32M, 32C, and 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is disposed above the four image forming units 20. The intermediate transfer belt 31 is supported so as to be rotatable in a predetermined direction (counterclockwise in FIG. 1), and serves as an intermediate transfer body onto which the toner images formed by each of the four image forming units 20 are sequentially superimposed and primarily transferred. The four image forming units 20 are disposed in a line from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31, in a so-called tandem arrangement.

[0019] The primary transfer units 32Y, 32M, 32C, and 32B are disposed above the image forming units 20Y, 20M, 20C, and 20B of the respective colors, with the intermediate transfer belt 31 sandwiched therebetween. The secondary transfer unit 33 is disposed upstream of the fixing unit 6 in the sheet conveying direction of the sheet conveying device 4, and downstream of the image forming units 20Y, 20M, 20C, and 20B of the respective colors in the rotation direction of the intermediate transfer belt 31 of the transfer unit 30. The belt cleaning unit 34 is disposed, for example, upstream of the image forming units 20Y, 20M, 20C, and 20B of the respective colors in the rotation direction of the intermediate transfer belt 31.

[0020] The toner images are primarily transferred at primary transfer units 32Y, 32M, 32C, and 32B for each color onto the outer circumferential surface of intermediate transfer belt 31. Then, as intermediate transfer belt 31 rotates, the toner images of the four image forming units 20 are successively superimposed and transferred onto intermediate transfer belt 31 at a predetermined timing, so that a color toner image is formed on the outer circumferential surface of intermediate transfer belt 31, in which toner images of four colors, yellow, magenta, cyan, and black, are superimposed.

[0021] The color toner image on the outer peripheral surface of the intermediate transfer belt 31 is transferred to the sheet S, which is fed synchronously by the sheet conveying device 4, at a secondary transfer nip formed in the secondary transfer unit 33. That is, the transfer unit 30 transfers the toner images formed on the surfaces of the four photosensitive drums 21 onto the sheet S via the intermediate transfer belt 31. The belt cleaning unit 34 removes and cleans the toner and the like remaining on the outer peripheral surface of the intermediate transfer belt 31 after the secondary transfer.

[0022] The fixing unit 6 is disposed downstream of the secondary transfer unit 33 in the sheet conveying direction of the sheet conveying device 4, and above the secondary transfer unit 33. The fixing unit 6 heats and pressurizes the sheet S onto which the toner image has been transferred, thereby fixing the toner image to the sheet S.

[0023] The sheet discharge section 7 is disposed above the transfer section 30. The sheet S on which the toner image has been fixed and printing has been completed is conveyed to the sheet discharge section 7.

[0024] The control unit 8 includes a CPU, an image processing unit, and other electronic circuits and electronic components (none of which are shown). The CPU controls the operation of each component provided in the image forming apparatus 1 based on control programs and data stored in the storage unit 9, and performs processing related to the functions of the image forming apparatus 1. The sheet supply unit 3, the sheet conveying device 4, the exposure unit 5, the image forming unit 20, the transfer unit 30, and the fixing unit 6 each receive individual commands from the control unit 8 and print on the sheet S in cooperation with each other.

[0025] The storage unit 9 is configured by combining a non-volatile storage device such as a program ROM (Read Only Memory) or a data ROM, and a volatile storage device such as a RAM (Random Access Memory).

[0026] Furthermore, the sheet transport device 4 includes a sheet detection unit 10 and a transport position adjustment mechanism 50 in addition to the sheet transport path 41. The sheet transport path 41 extends in a substantially vertical direction from the upstream side of the sheet detection unit 10 in the sheet transport direction to the downstream side of the transport position adjustment mechanism 50 in the sheet transport direction. The sheet transport path 41 also includes a plurality of transport roller pairs, including a first transport roller pair 42 and a second transport roller pair 43, which are arranged upstream of the transport position adjustment mechanism 50 in the sheet transport direction.

[0027] The sheet detection unit 10 is disposed on the sheet transport path 41, and is located upstream of the secondary transfer unit 33 of the transfer unit 30 in the sheet transport direction (below the secondary transfer unit 33 in FIG. 1). The sheet detection unit 10 includes, for example, a contact image sensor (CIS) 101 and a light source unit 102 (see FIG. 2). The contact image sensor 101 extends across the entire sheet width direction (depth direction in FIG. 1) that is perpendicular to the sheet transport direction of the sheet transport path 41.

[0028] The contact image sensor 101 detects the ends of the sheet S in the sheet conveyance direction (the vertical direction in FIG. 1) and the sheet width direction (the depth direction of the paper in FIG. 1) based on the difference in light intensity between the portion where light from the light source unit 102 is incident and the portion where the light is blocked by the sheet S. In this way, the sheet detection unit 10 detects the amount of inclination of the sheet S conveyed on the sheet conveyance path 41 with respect to the sheet conveyance direction Dc and the amount of positional deviation of the sheet S in the sheet width direction Dw.

[0029] The transport position adjustment mechanism 50 is disposed on the sheet transport path 41 upstream of the secondary transfer unit 33 of the transfer unit 30 in the sheet transport direction (below the secondary transfer unit 33 in FIG. 1) and downstream of the sheet detection unit 10 in the sheet transport direction (above the sheet detection unit 10 in FIG. 1). The transport position adjustment mechanism 50 has a function of transporting the sheet S and a function of correcting the transport position of the sheet S. More specifically, while transporting the sheet S, the transport position adjustment mechanism 50 performs skew correction to correct the inclination of the sheet S with respect to the sheet transport direction and position deviation correction to correct the position deviation of the sheet S in the sheet width direction based on the detection result of the sheet detection unit 10. The control unit 8 controls the transport position adjustment mechanism 50.

[0030] Next, the configuration of the transport position adjustment mechanism 50 will be described with reference to Figures 3 and 4 in addition to Figures 1 and 2. Figure 3 is a side view of the transport position adjustment mechanism 50 of the image forming apparatus 1 in Figure 1. Figure 4 is a bottom view of the transport position adjustment mechanism 50 in Figure 3. Note that the sheet transport direction Dc and the sheet width direction Dw are indicated in Figure 3 and subsequent figures.

[0031] As shown in Figures 3 and 4, the conveying position adjustment mechanism 50 includes an adjustment roller pair 51, a roller holder 52, a carriage 53, a roller drive motor 54, a skew correction motor 55, a position misalignment correction motor 56, and a reference position detection unit 57.

[0032] A plurality of adjustment roller pairs 51, for example, four pairs in this embodiment, are arranged in the sheet width direction Dw. The adjustment roller pair 51 has a drive roller 511 and a driven roller 512. The drive roller 511 is fixed to a rotation shaft 513 and rotated by a roller drive motor 54 via the rotation shaft 513. The driven roller 512 rotates in accordance with the rotation of the drive roller 511 as its circumferential surface comes into contact with the circumferential surface of the drive roller 511. The adjustment roller pair 51 nip and transport the sheet S.

[0033] Roller holder 52 rotatably supports rotation shaft 513 of drive roller 511 and rotation shaft 514 of driven roller 512. A swing support shaft 521 extending in a normal direction (a direction into the paper in FIG. 3, a vertical direction in FIG. 4) to the conveyance surface of sheet S is provided at one end side (a support end, left end side in FIGS. 3 and 4) of roller holder 52 in the sheet width direction Dw. The other end side (a swing end, right end side in FIGS. 3 and 4) of roller holder 52 in the sheet width direction Dw can swing in the sheet conveyance direction Dc relative to carriage 53 around swing support shaft 521.

[0034] The carriage 53 supports the roller holder 52. The carriage 53 is supported by the front frame 1a and the rear frame 1b of the image forming apparatus 1 so as to be movable in the sheet width direction Dw.

[0035] The roller drive motor 54 is provided on the support end side of the roller holder 52 in the sheet width direction Dw (the left end side in FIGS. 3 and 4). The roller drive motor 54 is connected to the rotation shaft 513 of the drive roller 511 via multiple gears. The roller drive motor 54 rotates and stops the rotation shaft 513. In other words, the roller drive motor 54 rotates and stops the drive roller 511.

[0036] The skew correction motor 55 is connected via multiple gears to a rack 522 provided at the swing end side of the roller holder 52 in the sheet width direction Dw (the right end side in FIGS. 3 and 4). The skew correction motor 55 swings the swing end side of the roller holder 52 in the sheet width direction Dw in the sheet conveyance direction Dc around the swing support shaft 521. In other words, the skew correction motor 55 changes the inclination of the roller holder 52 with respect to the sheet conveyance direction Dc. In other words, the skew correction motor 55 can tilt the adjustment roller pair 51 with respect to the sheet conveyance direction Dc.

[0037] The misalignment correction motor 56 is connected via a gear 56a to rack teeth (not shown) formed on one end edge 53a of the carriage 53 in the sheet conveyance direction Dc. The misalignment correction motor 56 moves the carriage 53 in the sheet width direction Dw. That is, the misalignment correction motor 56 can move the adjustment roller pair 51 in the sheet width direction Dw.

[0038] The roller drive motor 54, the skew correction motor 55, and the positional deviation correction motor 56 are each, for example, a stepping motor whose rotation direction and amount (rotation angle) can be precisely controlled by pulse control.

[0039] The reference position detection unit 57 is provided on the front frame 1a of the image forming apparatus 1. The reference position detection unit 57 is arranged, for example, on the front frame 1a and includes an optical sensor having a light-emitting unit and a light-receiving unit, and a light-shielding plate arranged on the roller holder 52 that appears and disappears in the optical path of the optical sensor. The reference position detection unit 57 detects the reference position of the roller holder 52. The reference position of the roller holder 52 is a position where the inclination with respect to the sheet conveying direction Dc is zero (perpendicular to the sheet conveying direction Dc) and where it is at the center of the sheet width direction Dw on the sheet conveying path 41.

[0040] The transport position adjustment mechanism 50 configured as described above can perform skew correction to correct the inclination of the sheet S with respect to the sheet transport direction Dc and positional deviation correction to correct the positional deviation of the sheet S in the sheet width direction Dw while transporting the sheet S with the adjustment roller pair 51. When correcting the skew of the sheet S, the transport position adjustment mechanism 50 uses the skew correction motor 55 to tilt the roller holder 52 (adjustment roller pair 51) with respect to the sheet transport direction Dc. When correcting the positional deviation of the sheet S, the transport position adjustment mechanism 50 uses the positional deviation correction motor 56 to move the roller holder 52 (adjustment roller pair 51) in the sheet width direction Dw.

[0041] Next, an example of the operation of skew correction and misalignment correction of the sheet S by the transport position adjustment mechanism 50 will be described. Figures 5 to 8 are schematic side views showing first to fourth stages of the progression of skew correction and misalignment correction by the transport position adjustment mechanism 50. Note that in Figures 5 to 8, the second transport roller pair 43 is not shown.

[0042] 5, before the sheet S being conveyed toward the secondary transfer unit 33 of the transfer unit 30 reaches the sheet detection unit 10, the roller holder 52 of the conveying position adjustment mechanism 50 is located at the reference position Pm0. That is, the roller holder 52 has an inclination of 0 with respect to the sheet conveying direction Dc (perpendicular to the sheet conveying direction Dc), and is located at the center of the sheet conveying path 41 in the sheet width direction Dw.

[0043] For example, as shown in Figure 5, if the sheet S is inclined at an angle α with respect to the reference position Ps0 (inclination with respect to the sheet conveying direction Dc is 0, and the center of the sheet width direction Dw on the sheet conveying path 41) and is misaligned by a distance β, the sheet detection unit 10 detects this inclination and misalignment of the sheet S.

[0044] 6, when the sheet S reaches the sheet detection unit 10, the sheet detection unit 10 uses a contact image sensor 101 to detect the amount of inclination of the sheet S conveyed toward the secondary transfer unit 33 of the transfer unit 30 with respect to the sheet conveyance direction Dc and the amount of positional deviation of the sheet S in the sheet width direction Dw. Detection information of the sheet S by the sheet detection unit 10 is sent to the control unit 8.

[0045] The control unit 8 controls the transport position adjustment mechanism 50 based on the detection information of the sheet S by the sheet detection unit 10. In detail, the control unit 8 derives a control signal for the transport position adjustment mechanism 50 based on the detection information of the sheet S detected by the sheet detection unit 10, and transmits the control signal to the transport position adjustment mechanism 50.

[0046] The control unit 8 moves the roller holder 52. More specifically, in the conveying position adjustment mechanism 50, the skew correction motor 55 is controlled to tilt the roller holder 52 at an angle α with respect to the sheet conveying direction Dc, and the position deviation correction motor 56 is controlled to move the roller holder 52 by a distance β in the sheet width direction Dw. The skew correction motor 55 and the position deviation correction motor 56 are, for example, stepping motors, and the rotation direction and rotation amount (rotation angle) are controlled by pulse control.

[0047] 7, when the sheet S reaches the conveying position adjustment mechanism 50, the control unit 8 performs skew correction and positional deviation correction. At this time, the sheet conveying path 41 holds and conveys the sheet S with the first conveying roller pair 42 arranged upstream of the adjustment roller pair 51 in the sheet conveying direction.

[0048] 8, the conveying position adjustment mechanism 50 returns the roller holder 52 to the reference position Pm0 while conveying the sheet S with the adjustment roller pair 51. As a result, the area of the sheet S held by the adjustment roller pair 51 moves to the reference position Ps0. Then, the control unit 8 sends the sheet S, which has been adjusted to an appropriate position on the sheet conveying path 41 by the conveying position adjustment mechanism 50, toward the secondary transfer unit 33 of the transfer unit 30. As a result, the entire sheet S moves to the reference position Ps0.

[0049] Next, the configuration of the sheet transport path 41 on the upstream side in the sheet transport direction of the transport position adjustment mechanism 50 will be described with reference to Figures 9 and 10. Figure 9 is a schematic front view of the curved portion 44 of the sheet transport path 41 of the image forming apparatus 1 in Figure 1. Figure 10 is a schematic front view of the curved portion 44 of the sheet transport path 41 in Figure 9, and shows a state when the transport position adjustment mechanism 50 is operated.

[0050] The sheet transport path 41 includes a first transport roller pair 42, a curved portion 44, a second transport roller pair 43, and a contact / separation mechanism 45 on the upstream side of the transport position adjustment mechanism 50 in the sheet transport direction Dc.

[0051] The first transport roller pair 42 is disposed upstream of the transport position adjustment mechanism 50 in the sheet transport direction Dc. The first transport roller pair 42 is configured by, for example, a drive roller 421 and a driven roller 422. The drive roller 421 is rotated by a motor (not shown). The driven roller 422 rotates in accordance with the rotation of the drive roller 421 by contacting its circumferential surface with that of the drive roller 421. The first transport roller pair 42 holds and transports the sheet S in a transport nip portion formed by contact between the drive roller 421 and the driven roller 422.

[0052] The curved portion 44 is disposed between the adjustment roller pair 51 and the first conveying roller pair 42. The curved portion 44 is curved in an S-shape so as to alternately protrude in the front and back directions of the sheet S from different positions in the sheet conveying direction Dc. More specifically, the downstream portion of the curved portion 44 in the sheet conveying direction Dc is curved so as to protrude leftward in FIG. 9, and the upstream portion of the curved portion 44 in the sheet conveying direction Dc is curved so as to protrude rightward in FIG. 9. That is, the curved portion 44 has an inflection portion 44a in approximately the center in the sheet conveying direction Dc. As a result, the region of the sheet conveying path 41 upstream of the adjustment roller pair 51 in the sheet conveying direction Dc is configured to be S-shaped when viewed from the sheet width direction, as shown in FIG.

[0053] The second conveying roller pair 43 is disposed at an inflection portion 44a of the curved portion 44. The second conveying roller pair 43 is configured by, for example, a drive roller 431 and a driven roller 432. The drive roller 431 is rotated by a motor (not shown). The driven roller 432 rotates in accordance with the rotation of the drive roller 431 by contacting its circumferential surface with that of the drive roller 431. The second conveying roller pair 43 holds and conveys the sheet S in a conveying nip portion formed by contact between the drive roller 431 and the driven roller 432.

[0054] The contact / separation mechanism 45 is disposed adjacent to the driven roller 432 of the second conveyor roller pair 43. The contact / separation mechanism 45 includes, for example, a biasing member 451 and a cam 452. The biasing member 451 is formed, for example, by a compression spring, and is connected between the shaft portion 432x of the driven roller 432 and the frame member of the main body 2. The biasing member 451 biases the shaft portion 432x in a direction in which the driven roller 432 approaches the drive roller 431.

[0055] The cam 452 comes into contact with, for example, the shaft portion 432x of the driven roller 432. The cam 452 rotates against the biasing force of the biasing member 451, and can move the shaft portion 432x in a direction in which the driven roller 432 moves away from the drive roller 431. In this way, the contact / separation mechanism 45 moves the drive roller 431 and the driven roller 432 that make up the second conveyor roller pair 43 toward or away from each other. The contact / separation mechanism 45 is controlled by the control unit 8.

[0056] The contact / separation mechanism 45 brings the drive roller 431 and the driven roller 432 into contact with each other when the transport position adjustment mechanism 50 transports the sheet S (see FIG. 9). The contact / separation mechanism 45 also separates the drive roller 431 and the driven roller 432 when the transport position adjustment mechanism 50 corrects the transport position of the sheet S (see FIG. 10).

[0057] According to the above configuration, when the transport position adjustment mechanism 50 is operated to perform skew correction and misalignment correction, the adjustment roller pair 51 holds and transports the sheet S together with the first transport roller pair 42. As a result, the sheet S held by the adjustment roller pair 51 and the first transport roller pair 42 is bent into an S-shape when viewed in the sheet width direction. The sheet S is bent and curved so as to protrude in two directions, thereby sufficiently eliminating tension, bending, and twisting. Therefore, when the sheet S transported along the sheet transport path 41 is adjusted to an appropriate position on the sheet transport path 41, the adjustment can be made without applying a load to the sheet S.

[0058] Furthermore, the sheet transport device 4 includes the second transport roller pair 43 and the contact / separation mechanism 45 configured as described above. With this configuration, even in a sheet transport path 41 that is suitable for transporting small-sized sheets S, the contact / separation mechanism 45 can separate the drive roller 431 and the driven roller 432, thereby enabling skew correction and misalignment correction. Therefore, in sheet transport devices 4 having a variety of configurations, it is possible to adjust the sheet S to an appropriate position on the sheet transport path 41 without applying a load to the sheet S.

[0059] 11 is a schematic front view of a curved portion 44 of a modified sheet transport path 41. The modified sheet transport path 41 includes a contact / separation mechanism 46. The contact / separation mechanism 46 is disposed adjacent to the driven roller 432 of the second transport roller pair 43.

[0060] The contact / separation mechanism 46 moves at least one of the drive roller 431 and the driven roller 432 of the second conveyance roller pair 43 in the sheet conveyance direction Dc to separate them. In the present embodiment, the contact / separation mechanism 46 moves the driven roller 432 downstream in the sheet conveyance direction Dc to separate the drive roller 431 and the driven roller 432. Note that the drive roller 431 may be moved in the sheet conveyance direction Dc, or both the drive roller 431 and the driven roller 432 may be moved in the sheet conveyance direction Dc. A portion of each of the separated drive roller 431 and the driven roller 432 protrudes inside the sheet conveyance path 41.

[0061] According to the configuration of the modified example, the driven roller 432 moved downstream in the sheet conveying direction Dc can enhance the effect of bending and warping the sheet S so that it protrudes in the front-to-back direction at the curved portion 44. Therefore, when adjusting the sheet S to an appropriate position on the sheet conveying path 41, it is possible to improve the effect of eliminating tension, bending, and twisting.

[0062] The image forming apparatus 1 also includes the sheet conveying device 4 having the above-described configuration that conveys the sheet S to the transfer unit 30. With this configuration, the image forming apparatus 1 can adjust the sheet S to an appropriate position on the sheet conveying path 41 without applying a load to the sheet S before transferring the image onto the sheet S. Therefore, it is possible to achieve a suitable transfer of the image onto the sheet S.

[0063] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and various modifications can be made without departing from the spirit of the invention.

[0064] For example, in the above embodiment, the image forming apparatus 1 is a so-called tandem type image forming apparatus for color printing that forms images of multiple colors by sequentially overlapping them, but the image forming apparatus is not limited to this type. The image forming apparatus may be a non-tandem type image forming apparatus for color printing or a monochrome image forming apparatus.

[0065] The sheet conveying device 4 can also be mounted on an inkjet recording type image forming device, a sheet post-processing device that performs post-processing on a sheet after image formation, or the like. [Industrial Applicability]

[0066] The present invention can be used in a sheet transport device and an image forming apparatus. [Explanation of symbols]

[0067] 1. Image forming device 4 Sheet transport device 10 Sheet detection unit 20 Image forming unit 30 Transfer unit 41 Sheet transport path 42 First conveying roller pair 43 Second conveying roller pair 44 Curved section 45, 46 Approach / separation mechanism 50 Transfer position adjustment mechanism 51 Adjustment roller pair 55 Deskew Motor 56 Position correction motor Dc Sheet transport direction Dw Sheet width direction S seat

Claims

1. a sheet detection unit disposed on the sheet conveying path and configured to detect an amount of inclination of a conveyed sheet with respect to a sheet conveying direction and an amount of positional deviation of the sheet in a sheet width direction perpendicular to the sheet conveying direction; a conveyance position adjustment mechanism that is disposed on the sheet conveyance path downstream of the sheet detection unit in the sheet conveyance direction, and that corrects the conveyance position of the sheet by performing skew correction to correct an inclination of the sheet with respect to the sheet conveyance direction and positional deviation correction to correct a positional deviation of the sheet in the sheet width direction based on a detection result of the sheet detection unit while conveying the sheet; Equipped with The transport position adjustment mechanism includes: a pair of adjustment rollers that nip and transport the sheet; a skew correction motor that tilts the pair of adjustment rollers with respect to the sheet conveying direction; a positional deviation correction motor that moves the pair of adjustment rollers in the sheet width direction; Equipped with The sheet transport path includes: a first conveyance roller pair disposed upstream of the conveyance position adjustment mechanism in the sheet conveyance direction; curved portions that are arranged between the adjustment roller pair and the first conveying roller pair and are curved in an S shape so as to alternately protrude in a front and back direction of the sheet from different positions in the sheet conveying direction; a second conveying roller pair disposed at an inflection portion of the curved portion; a contact / separation mechanism that brings the two transport rollers constituting the second transport roller pair into contact with and separates the two transport rollers from one another; Equipped with the adjustment roller pair, together with the first transport roller pair, holds and transports the sheet; The sheet conveying device is characterized in that the contact / separation mechanism brings the two conveying rollers into contact when the sheet is conveyed by the conveying position adjustment mechanism, and separates the two conveying rollers when the conveying position adjustment mechanism corrects the conveying position of the sheet.

2. The contact / separation mechanism moves at least one of the two transport rollers in the sheet transport direction to separate them, 2. The sheet transport device according to claim 1, wherein a portion of each of the two spaced apart transport rollers protrudes inward of the sheet transport path.

3. An image forming unit that forms an image; a transfer unit that transfers the image onto the sheet; the sheet conveying device according to claim 1 or 2, which conveys the sheet to the transfer section; An image forming apparatus comprising:

Images