Sheet conveying device and image forming apparatus

Abstract

To achieve higher skew correction accuracy for various sheets.SOLUTION: A first roller pair, a second roller pair disposed downstream of the first roller pair, a third roller pair disposed downstream of the second roller pair, and a controller, wherein a moving direction of the sheet at a nip portion of the first roller pair is a first direction, and a moving direction of the sheet at a nip portion of the second roller pair is a second direction, when a moving direction of the sheet at the nip portion of the third roller pair is a third direction, an angle between the first direction and the second direction is larger than an angle between the second direction and the third direction, and the controller is configured to execute a first mode of performing skew correction of the sheet by causing the leading edge of the sheet to abut against the second roller pair in a stopped state and a second mode of performing skew correction of the sheet by causing the leading edge of the sheet to abut against the third roller pair in a stopped state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In recent years, the sheets used as recording materials in image forming devices have become more diverse, and there is a demand for them to be able to handle a wide range of sheet materials, for example, those with significantly different basis weights. Patent Document 1 describes an image forming device that corrects skew by abutting the leading edge of a sheet against a nip between a pair of registration rollers. In this image forming device, the conveyance path is curved upstream of the pair of registration rollers, and during skew correction, the sheet bends toward the outside of the curve of the conveyance path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-189367 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned document, regardless of the basis weight or material of the sheet, skew correction is performed by bending the sheet in the conveyance path between the registration roller pair and the conveyance roller pair upstream of the registration roller pair. However, with this configuration, it is sometimes difficult to obtain sufficient skew correction accuracy for both sheets with high rigidity such as thick paper and sheets with low rigidity such as thin paper.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sheet conveying device and an image forming apparatus that can achieve higher skew correction accuracy for a variety of sheets. [Means for solving the problem]

[0006] One aspect of the present invention is a sheet conveying device including a first roller pair that conveys a sheet, a second roller pair that is disposed downstream of the first roller pair in a sheet conveying path and conveys the sheet, a third roller pair that is disposed downstream of the second roller pair in the conveying path and conveys the sheet, and a control unit, wherein when a moving direction of the sheet at a nip portion of the first roller pair is defined as a first direction, a moving direction of the sheet at a nip portion of the second roller pair is defined as a second direction, and a moving direction of the sheet at a nip portion of the third roller pair is defined as a third direction, an angle between the first direction and the second direction is larger than an angle between the second direction and the third direction, and the control unit controls the sheet to stop a leading edge of the sheet. This sheet conveying device is capable of executing a first mode in which the leading edge of the sheet is pushed against the second pair of rollers in a stopped state to correct the skew of the sheet, and then the leading edge of the sheet passes through the third pair of rollers in a stopped state without pushing against the third pair of rollers in a stopped state, and a second mode in which the leading edge of the sheet passes through the second pair of rollers without pushing against the second pair of rollers in a stopped state, and then the leading edge of the sheet is pushed against the third pair of rollers in a stopped state to correct the skew of the sheet, and the control unit executes the first mode when conveying a sheet having a first basis weight, and executes the second mode when conveying a sheet having a second basis weight smaller than the first basis weight.

[0007] Another aspect of the present invention is a sheet conveying device including a first roller pair that conveys a sheet, a second roller pair that is disposed downstream of the first roller pair in a sheet conveying path and conveys the sheet, a third roller pair that is disposed downstream of the second roller pair in the conveying path and conveys the sheet, and a control unit, wherein when a moving direction of the sheet at a nip portion of the first roller pair is defined as a first direction, a moving direction of the sheet at a nip portion of the second roller pair is defined as a second direction, and a moving direction of the sheet at a nip portion of the third roller pair is defined as a third direction, an angle between the first direction and the second direction is smaller than an angle between the second direction and the third direction, and the control unit controls the leading edge of the sheet to be conveyed. This sheet conveying device is capable of executing a first mode in which the leading edge of the sheet passes through the second pair of rollers without hitting the second pair of rollers, which are stopped, and then hits the third pair of rollers, which are stopped, to correct the skew of the sheet; and a second mode in which the leading edge of the sheet hits the second pair of rollers, which are stopped, to correct the skew of the sheet, and then passes through the third pair of rollers without hitting the third pair of rollers, which are stopped, and the control unit executes the first mode when conveying a sheet having a first basis weight, and executes the second mode when conveying a sheet having a second basis weight smaller than the first basis weight.

[0008] Another aspect of the present invention is a sheet conveying device including a first roller pair that conveys a sheet, a second roller pair that is disposed downstream of the first roller pair in a sheet conveying path and conveys the sheet, a third roller pair that is disposed downstream of the second roller pair in the conveying path and conveys the sheet, and a control unit, wherein when a moving direction of the sheet at a nip portion of the first roller pair is defined as a first direction, a moving direction of the sheet at a nip portion of the second roller pair is defined as a second direction, and a moving direction of the sheet at a nip portion of the third roller pair is defined as a third direction, an angle between the first direction and the second direction is larger than an angle between the second direction and the third direction, and the control unit controls the sheet conveying device to convey the sheet. and a second mode in which the leading edge of the sheet passes through the second pair of rollers without abutting against the second pair of rollers, which is stopped, to correct the skew of the sheet, and then the leading edge of the sheet is abutted against the third pair of rollers, which is stopped, to correct the skew of the sheet, and the control unit executes the first mode when conveying a first sheet, and executes the second mode when conveying a second sheet having lower rigidity than the first sheet. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a sheet conveying device and an image forming apparatus that can achieve higher skew correction accuracy for a variety of sheets. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of a cash register unit according to an embodiment. [Figure 3] FIG. 4 is a schematic diagram illustrating the positional relationship between roller pairs according to the embodiment. [Figure 4] 10A to 10E are explanatory diagrams of a cardboard mode according to an embodiment. [Figure 5] 10A to 10E are explanatory diagrams of a thin paper mode according to an embodiment. [Figure 6] 10 is a flowchart showing the procedure of a print job according to an embodiment. [Figure 7] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] First, we will explain the overall configuration of an image forming apparatus 1 according to this embodiment. Figure 1 is a schematic diagram showing the cross-sectional configuration of the image forming apparatus 1. The image forming apparatus 1 includes an image forming apparatus main body 1A and a sheet feeding device 2 connected to the image forming apparatus main body 1A.

[0013] The image forming apparatus 1 uses the image forming unit 1B to form an image on the sheet S while conveying the sheet S one by one. As the sheet, which is the recording material (recording medium), a variety of sheet materials of different sizes and materials can be used, including paper such as plain paper and cardboard, surface-treated sheet materials such as coated paper, specially shaped sheet materials such as envelopes and index paper, plastic film, cloth, etc.

[0014] The image forming apparatus main body 1A has an image forming unit 1B of a tandem intermediate transfer type in which four process units 513 are lined up along an intermediate transfer belt 506 that serves as an intermediate transfer body. Compared to the direct transfer type, the intermediate transfer type has the advantage of being able to easily handle a variety of sheets S, such as ultra-thick paper and coated paper, because it does not need to hold the sheet S on a transfer drum or transfer belt. In addition, the tandem intermediate transfer type is suited to achieving high productivity due to its features of parallel processing in multiple process units 513 and simultaneous transfer of a full-color image formed by overlapping toner images of multiple colors.

[0015] The image forming unit 1B is an example of an image forming means that forms an image on the sheet S, and may use a direct transfer type electrophotographic unit in which a toner image formed on the photosensitive drum 508 is transferred to the sheet S without using an intermediate transfer body. The image forming means is not limited to an electrophotographic type, and may be, for example, an inkjet type print unit.

[0016] Each process unit 513 has a photosensitive drum 508 as an image carrier, a charging device, an exposure device 511, a developing device 510, and a cleaning device 509. An intermediate transfer belt 506 is stretched around a drive roller 504, a tension roller 505, and an inner secondary transfer roller 503, and is driven to be transported in the direction of arrow B in the figure. A primary transfer roller 507 is disposed on the inner circumferential side of the intermediate transfer belt 506 at a position corresponding to each photosensitive drum 508. Furthermore, a secondary transfer roller 56 is disposed on the outer circumferential side of the intermediate transfer belt 506 at a position facing the inner secondary transfer roller 503 with the intermediate transfer belt 506 sandwiched therebetween.

[0017] In addition, the image forming apparatus main body 1A has an internal feeding section 51, an intermediate conveying section 54, a pre-registration conveying section 50, a skew correction section 55, a pre-fixing conveying section 57, a fixing device 58, a branching conveying section 59, an inversion discharge section 550, a double-sided inversion section 501, and a double-sided conveying section 502.

[0018] The flow of the image forming operation will be described below. Here, it is assumed that the sheet S is fed from the main body feed unit 51.

[0019] The sheets S are stored in a storage cabinet in a state where they are stacked on a lift-up device 52 provided in the internal feeding section 51. The sheets S are fed one by one by a feeding unit 53 of the internal feeding section 51 in accordance with the operation timing of the image forming section 1B. The feeding unit 53 can be an air suction type that uses negative pressure generated by a fan to attract and convey the sheet S to a belt, or a roller type that uses the frictional force of a roller that rotates in contact with the sheet S. The feeding unit 53 in FIG. 1 is an air suction type. The sheet S fed by the feeding unit 53 passes through the intermediate conveying section 54 and the pre-registration conveying section 50, and is conveyed to the skew correction section 55.

[0020] A detection unit S10 that detects the leading edge of the sheet S is disposed in the pre-registration conveying unit 50. Based on the detection result of the detection unit S10, a delay time of the sheet S relative to a reference conveying timing is measured, and the conveying speed of the sheet S is controlled accordingly to cancel the delay time. After skew correction is performed in the skew correction unit 55, the sheet S is sent to the secondary transfer unit. The secondary transfer unit is a nip formed between a secondary transfer roller 56 and an intermediate transfer belt 506.

[0021] In parallel with the transport of the sheet S to the secondary transfer unit described above, a toner image is formed in the image forming unit 1B. The photosensitive drum 508 and the intermediate transfer belt 506 are rotated in predetermined directions A and B. In each process unit 513, the surface of the photosensitive drum 508 is charged by a charging device. The exposure device 511 exposes the photosensitive drum 508 based on image information and writes an electrostatic latent image on the surface of the photosensitive drum 508. The development device 510 supplies toner as a developer to the photosensitive drum 508 and develops the electrostatic latent image into a single-color toner image of yellow, magenta, cyan, or black. These single-color toner images are primarily transferred from the photosensitive drum 508 to the intermediate transfer belt 506 by the primary transfer roller 507. At this time, the four single-color toner images are superimposed on each other on the intermediate transfer belt 506, forming a full-color image on the intermediate transfer belt 506. Residual toner that has not been transferred to the intermediate transfer belt 506 and remains on the photosensitive drum 508 is removed by a cleaning device 509 .

[0022] The full-color image is conveyed to a secondary transfer unit by the rotation of the intermediate transfer belt 506. Then, in the secondary transfer unit, the toner image is transferred from the intermediate transfer belt 506 to the sheet S by applying a voltage to the secondary transfer roller 56.

[0023] The sheet S that has passed through the secondary transfer unit is transported to a fixing device 58 by a pre-fixing transport unit 57. The fixing device 58 heats the image on the sheet S with heat emitted from a heat source such as a halogen lamp while nipping and transporting the sheet S, for example, with a pair of rollers, thereby fixing the image on the sheet S. The sheet S that has passed through the fixing device 58 is either discharged directly toward a discharge tray 500 by a branching transport unit 59, or guided to a reversing discharge unit 550. The image forming apparatus 1 can discharge the sheet S to the discharge tray 500 in a state in which the reversing discharge unit 550 reverses the sheet S so that the side on which the image has been transferred in the secondary transfer unit faces down (face down).

[0024] In the case of double-sided printing in which images are formed on both sides of the sheet S, the sheet S with an image formed on its first side is sent from the branch conveying section 59 through the reverse discharge section 550 to the double-sided reversing section 501. The sheet S is then switched back in the double-sided reversing section 501 and sent again to the intermediate conveying section 54 via the double-sided conveying section 502. After this, an image is formed on the second side in the same manner as on the first side, and the sheet S is then discharged to the discharge tray 500.

[0025] The sheet fed from the sheet feeding device 2, which will be described later, is conveyed to the pre-register conveying section 50 via a conveying path 54c of the intermediate conveying section 54. The operation after the pre-register conveying section 50 is the same as when the sheet S is fed from the main body conveying section 51.

[0026] <Sheet feeding device> The sheet feeding device 2 according to this embodiment will be described. In this embodiment, the sheet feeding device 2 feeds sheets S toward the image forming apparatus main body 1A. As shown in FIG. 1, the sheet feeding device 2 according to this embodiment has three vertically arranged sheet feeding sections 60U, 60M, and 60L, and a registration unit (hereinafter referred to as a registration unit 240) that corrects skew of the sheets S. The registration unit 240 is an example of a sheet conveying device.

[0027] The sheet feeding sections 60U, 60M, and 60L have the same configuration as the main body feeding section 51. That is, each of the sheet feeding sections 60U, 60M, and 60L has a storage case having a lift-up device, and a feeding unit that feeds sheets S one by one from the storage case.

[0028] Sheets S fed from the upper and middle sheet feeding units 60U, 60M are transported through an upper transport path α. Sheets fed from the lower sheet feeding unit 60L are transported through a lower transport path β. The upper transport path α and the lower transport path β merge at the registration unit 240 to form a horizontal path γ. The horizontal path γ extends in a substantially horizontal direction and communicates with the transport path 54c of the image forming apparatus main body 1A. Therefore, sheets S fed from each sheet feeding unit 60U, 60M, 60L are transported to the image forming apparatus main body 1A via the registration unit 240.

[0029] Similar to the internal feeding unit 51 of the image forming apparatus main body 1A, during image formation operation, a sheet S is fed from one of the sheet feeding units 60U, 60M, 60L in accordance with the operation timing of the image forming unit 1B. A second conveyance sensor S2 that detects the leading edge of the sheet S is disposed on the horizontal path γ. The control unit of the image forming apparatus 1 temporarily stops the conveyance of the sheet S based on the detection of the leading edge of the sheet by the second conveyance sensor S2, and resumes the conveyance of the sheet S in accordance with the operation timing of the image forming unit 1B. This allows the sheet S to be fed to the image forming apparatus main body 1A in a state where variations in the conveyance timing that occur inside the sheet feeding device 2 have been corrected.

[0030] <Register unit> Next, the registration unit 240 according to this embodiment will be described. Fig. 2 is a cross-sectional view of the registration unit 240. As shown in Fig. 2, the registration unit 240 has a first registration roller pair (hereinafter referred to as a first registration roller pair 243) and a second registration roller pair (hereinafter referred to as a second registration roller pair 244). The registration unit 240 also has an upper conveyance roller pair 245 and a lower conveyance roller pair 246.

[0031] The upper conveying roller pair 245 is an example of a first roller pair that conveys the sheet S. The first registration roller pair 243 is an example of a second roller pair that is arranged downstream of the first roller pair in the conveying path of the sheet S and conveys the sheet S. The second registration roller pair 244 is an example of a third roller pair that is arranged downstream of the second roller pair in the conveying path of the sheet S and conveys the sheet S.

[0032] When the upper conveying path α and the horizontal path γ are defined as a first conveying path, the lower conveying roller pair 246 is an example of a fourth roller pair arranged on a second conveying path (lower conveying path β) that merges with the first conveying path. Note that in the case of a sheet feeding device 2 that does not have the upper conveying path α, the lower conveying roller pair 246 can be called the first roller pair.

[0033] The first registration roller pair 243 and the second registration roller pair 244 are disposed on the horizontal path γ. The second registration roller pair 244 is located downstream of the first registration roller pair 243 in the sheet conveying direction on the horizontal path γ.

[0034] The upper conveying roller pair 245 is disposed on the upper conveying path α and is located upstream of the first registration roller pair 243 in the sheet conveying direction on the upper conveying path α. The lower conveying roller pair 246 is disposed on the lower conveying path β and is located upstream of the first registration roller pair 243 in the sheet conveying direction on the lower conveying path β.

[0035] Each roller pair (243, 244, 245, 246) is composed of a drive roller that is rotated by the driving force of a conveying motor M1 (FIG. 7), and a driven roller that forms a nip N3, N4, N5, N6 together with the drive roller and rotates following the drive roller. In this embodiment, one conveying motor M1 is provided for each roller pair so that the rotation of each roller pair (243, 244, 245, 246) can be controlled independently. In addition, each roller pair (243, 244, 245, 246) is configured so that the drive roller and the driven roller can be brought into contact with and separated from each other (the nip can be opened and closed) by the driving force of a separating motor M2 (FIG. 7). In this embodiment, one separating motor M2 is provided for each roller pair so that the opening and closing of each roller pair (243, 244, 245, 246) can be controlled independently. Furthermore, the second registration roller pair 244 is configured to be shiftable in the sheet width direction by the driving force of a shift motor M3 (FIG. 7). The sheet width direction is a direction parallel to the rotation axis of the second registration roller pair 244. The shift motor M3 functions as a moving unit for moving the second registration roller pair 244 (third roller pair) in the sheet width direction based on the detection result of the lateral registration sensor S3.

[0036] Between the upper conveying roller pair 245 and the first registration roller pair 243, an upper conveying path α is formed by an upper guide 301a (first guide) and a lower guide 301b (second guide). The upper conveying path α is curved between the upper conveying roller pair 245 and the first registration roller pair 243, such that the lower guide 301b is located on the outer side of the curve and the upper guide 301a is located on the inner side of the curve. The distance between the lower guide 301b (outer guide) and the upper guide 301a (inner guide) is wider in the intermediate portion between the upper conveying roller pair 245 and the first registration roller pair 243 than in the vicinity of the upper conveying roller pair 245 and the vicinity of the first registration roller pair 243. Therefore, a space α1 is formed in the intermediate portion between the upper conveying roller pair 245 and the first registration roller pair 243, allowing the sheet S to bend (form a loop) toward the outer side of the curve of the upper conveying path α.

[0037] Between the lower conveying roller pair 246 and the first registration roller pair 243, a lower conveying path β is formed by an upper guide 302a and a lower guide 302b. The lower conveying path β is curved between the lower conveying roller pair 246 and the first registration roller pair 243 such that the lower guide 302b is located on the inside of the curve and the upper guide 302a is located on the inside of the curve. The distance between the lower guide 302b (inner guide) and the upper guide 302a (outer guide) is wider in the intermediate portion between the lower conveying roller pair 246 and the first registration roller pair 243 than in the vicinity of the lower conveying roller pair 246 and the vicinity of the first registration roller pair 243. Therefore, a space β1 is formed in the intermediate portion between the lower conveying roller pair 246 and the first registration roller pair 243, allowing the sheet S to bend (form a loop) toward the outside of the curve of the lower conveying path β.

[0038] The upper conveying path α and the lower conveying path β join together near the upstream side of the first registration roller pair 243. The conveying path downstream of the joining point of the upper conveying path α and the lower conveying path β is formed by an upper guide 303a and a guide 303b.

[0039] Between the first pair of registration rollers 243 and the second pair of registration rollers 244, a horizontal path γ is formed by an upper guide 304a (third guide) and a lower guide 304b (fourth guide). A portion of the upper guide 304a is recessed upward. In other words, the upper guide 304a has a recessed portion (retracted portion) in which a portion of the upper guide 304a in the sheet conveying direction is recessed away from the lower guide 304b (retracted). As a result, a space γ1 is formed between the first pair of registration rollers 243 and the second pair of registration rollers 244, which allows the sheet S to bend upward (to form a loop).

[0040] The registration unit 240 also has a first conveyance sensor S1, a second conveyance sensor S2, and a lateral registration sensor S3. The first conveyance sensor S1 is disposed near the upstream side of the first registration roller pair 243. The second conveyance sensor S2 and the lateral registration sensor S3 are disposed near the upstream side of the second registration roller pair 244.

[0041] The first conveyance sensor S1 and the second conveyance sensor S2 are used to acquire the passing timing of the leading and trailing edges of the sheet S in order to control the sheet conveyance operation. The first conveyance sensor S1 is used, for example, for conveyance control (control of loop amount) when correcting skew by abutting the leading edge of the sheet S against the nip portion N2 of the first registration roller pair 243. The second conveyance sensor S2 is used, for example, for conveyance control (control of loop amount) when correcting skew by abutting the leading edge of the sheet S against the nip portion N3 of the second registration roller pair 244.

[0042] The lateral registration sensor S3 is, for example, a CIS (contact image sensor) type line sensor having light-receiving elements arranged in the sheet width direction. The lateral registration sensor S3 functions as a position detection unit capable of acquiring information on the edge position of the sheet S in the sheet width direction. The lateral registration sensor S3 is used to align (laterally register) the image formed by the image forming unit 1B with respect to the sheet width direction (main scanning direction). In this embodiment, horizontal registration is performed by shifting the second registration roller pair 244 in the sheet width direction while the second registration roller pair 244 is sandwiching the sheet S based on the detection result of the lateral registration sensor S3. Note that the horizontal registration method may be a method in which the image forming position (for example, the latent image writing start position during exposure) by the image forming unit 1B is changed in accordance with the position of the sheet S detected by the lateral registration sensor S3 or the like.

[0043] <Positional relationship of roller pairs in the registration unit> The positional relationship between the roller pairs in the registration unit 240 will be described with reference to Fig. 3. Fig. 3 is a schematic diagram showing the registration unit 240 as viewed in the sheet width direction.

[0044] In the following description, nip lines L1, L2, L3, and L4 are defined as follows: The nip line L1 of the upper conveying roller pair 245 passes through the nip portion N1 of the upper conveying roller pair 245 and is a straight line perpendicular to the line connecting the rotation axes of the two rollers 245a and 245b that constitute the upper conveying roller pair 245. The nip line L2 of the first registration roller pair 243 passes through the nip portion N2 of the first registration roller pair 243 and is a straight line perpendicular to the line connecting the rotation axes of the two rollers 243a and 243b that constitute the first registration roller pair 243. The nip line L3 of the second registration roller pair 244 passes through the nip portion N3 of the second registration roller pair 244 and is a straight line perpendicular to the line connecting the rotation axes of the two rollers 244a and 244b that constitute the second registration roller pair 244. The nip line L4 of the lower conveying roller pair 246 is a straight line that passes through the nip portion N4 of the lower conveying roller pair 246 and is perpendicular to the straight line connecting the rotation axes of the two rollers 246a and 246b that make up the lower conveying roller pair 246. Each of the nip lines L1 to L4 may be said to be a tangent to the roller pairs (245, 243, 244, 246) at the nip portions N1 to N4.

[0045] The movement direction of the sheet S in the nip portion N1 of the upper conveying roller pair 245 is referred to as the nip line direction D1 of the upper conveying roller pair 245. The movement direction of the sheet S in the nip portion N2 of the first registration roller pair 243 is referred to as the nip line direction D2 of the first registration roller pair 243. The movement direction of the sheet S in the nip portion N3 of the second registration roller pair 244 is referred to as the nip line direction D3 of the second registration roller pair 244. The movement direction of the sheet S in the nip portion N4 of the lower conveying roller pair 246 is referred to as the nip line direction D4 of the lower conveying roller pair 246. The nip line directions D1, D2, D3, and D4 are parallel to the nip lines L1, L2, L3, and L4, respectively.

[0046] The angle between the nip line direction D1 of the upper conveying roller pair 245 and the nip line direction D2 of the first registration roller pair 243 is defined as θ1. Similarly, the angle between the nip line direction D2 of the first registration roller pair 243 and the nip line direction D3 of the second registration roller pair 244 is defined as θ2. The angle between the nip line direction D4 of the lower conveying roller pair 246 and the nip line direction D2 of the first registration roller pair 243 is defined as θ3. The angles θ1, θ2, and θ3 are all greater than or equal to 0° and less than 360°.

[0047] The angles θ1, θ2, and θ3 can be considered to be the angle between the direction vector of nip line L1 and the direction vector of nip line L2, the angle between the direction vector of nip line L2 and the direction vector of nip line L3, and the angle between the direction vector of nip line L4 and the direction vector of nip line L2, respectively. Angle θ1 is one of the angles formed between the nip line L1 of the upper conveying roller pair 245 and the nip line L2 of the first registration roller pair 243. Angle θ2 is one of the angles formed between the nip line L2 of the first registration roller pair 243 and the nip line L3 of the second registration roller pair 244. Angle θ3 is one of the angles formed between the nip line L4 of the lower conveying roller pair 246 and the nip line L2 of the first registration roller pair 243.

[0048] In this embodiment, the magnitude relationships among the angles θ1, θ2, and θ3 are θ1>θ2 and θ3>θ2. In this embodiment, the values ​​of the angles θ1, θ2, and θ3 are, for example, θ1=90°, θ2=7°, and θ3=78°, but are not limited to these values.

[0049] That is, the amount of change (θ1) in the movement direction of the sheet S in the section from the upper conveying roller pair 245 to the first registration roller pair 243 is larger than the amount of change (θ2) in the movement direction of the sheet S in the section from the first registration roller pair 243 to the second registration roller pair 244. In other words, the curved angle of the upper conveying path α in the section from the upper conveying roller pair 245 to the first registration roller pair 243 is larger than the curved angle of the horizontal path γ in the section from the first registration roller pair 243 to the second registration roller pair 244. Furthermore, the amount of change (θ3) in the movement direction of the sheet S in the section from the lower conveying roller pair 246 to the first registration roller pair 243 is larger than the amount of change (θ2) in the movement direction of the sheet S in the section from the first registration roller pair 243 to the second registration roller pair 244. In other words, the curve angle of the lower conveying path β in the section from the lower conveying roller pair 246 to the first registration roller pair 243 is larger than the curve angle of the horizontal path γ in the section from the first registration roller pair 243 to the second registration roller pair 244.

[0050] <Correction operation> In this embodiment, the correction operation performed by the registration unit 240 will be described separately for a sheet S with high rigidity such as thick paper and a sheet S with low rigidity such as thin paper. Hereinafter, the mode (first mode) of the correction operation for a sheet S with high rigidity will be referred to as the "thick paper mode," and the mode (second mode) of the correction operation for a sheet S with low rigidity will be referred to as the "thin paper mode."

[0051] The registration unit 240 of this embodiment performs correction operations including skew correction of the sheet S and correction of the sheet position in the sheet width direction (horizontal registration). The following describes a case where the sheet S is transported via the upper transport path α, but the same description also applies to a case where the sheet S is transported via the lower transport path α by replacing the "upper transport roller pair 245" with the "lower transport roller pair 246."

[0052] (Cardboard mode) 4(a) to 4(e) are diagrams showing the correction operation of the registration unit 240 in the cardboard mode. The order of FIGS. 4(a) to 4(d) is the same as the chronological order of the correction operation. FIG. 4(e) is a schematic diagram of the registration unit 240 seen from above at the same time as FIG. 4(d).

[0053] 4A, the sheet S is conveyed from the upper conveying roller pair 245 through the upper conveying path α toward the first registration roller pair 243. At this point, the first registration roller pair 243 is not rotated and is in a stopped state. The stopped state of the first registration roller pair 243 is maintained until a predetermined time has elapsed even after the leading edge of the sheet S is detected by the first conveying sensor S1.

[0054] While the first registration roller pair 243 is stopped, the leading edge of the sheet S abuts against the nip portion N2 of the first registration roller pair 243, and the upper conveying roller pair 245 continues to convey the sheet S even after the abutment. As a result, as shown in FIG. 4(b), a flexure (loop L) of the sheet S is formed between the upper conveying roller pair 245 and the first registration roller pair 243. At this time, the formation of the loop L is permitted by the space α1 (FIG. 2) on the side of the lower guide 301b of the above-mentioned upper conveying path α. Note that when the sheet is conveyed via the lower conveying path β, the formation of the loop L is permitted by the space β1 on the side of the upper guide 302a.

[0055] When a loop L is formed in the sheet S, stress is generated in the sheet S to resolve the loop L. This stress causes the leading edge of the sheet S to pivot so as to follow the nip portion N2 of the first registration roller pair 243. In other words, if the sheet S is skewed (the leading edge of the sheet is tilted relative to the sheet width direction), one of the two corners of the leading edge of the sheet S (the leading edge) reaches the nip portion N2 earlier than the other (the lagging edge). Thereafter, as the loop L is formed, the leading edge of the sheet S pivots so that the corner on the lagging edge moves downstream in the sheet conveyance direction, with the corner on the leading edge as a fulcrum, and the skew of the sheet S is corrected.

[0056] 4C, the first registration roller pair 243 starts to rotate, and the first registration roller pair 243 starts to convey the sheet S. After the first registration roller pair 243 starts to be driven, the nip portion N1 of the upper conveying roller pair 245 is opened. By opening the nip portion N2 of the upper conveying roller pair 245, it is possible to prevent an increase in conveying resistance caused by the loop L of the sheet S rubbing against the lower guide 301b.

[0057] After the first pair of registration rollers 243 starts conveying the sheet S, the position of the sheet edge in the sheet width direction is detected by the lateral registration sensor S3 (FIG. 4(d)). Then, as shown in FIG. 4(e), based on the detection result of the lateral registration sensor S3, while the second pair of registration rollers 244 is nipping and conveying the sheet S, the second pair of registration rollers 244 is shifted in the sheet width direction. While the second pair of registration rollers 244 is shifting, the nip portions N2 and N1 of the first pair of registration rollers 243 and the upper conveying roller pair 245, which are upstream of the second pair of registration rollers 244, are opened, thereby reducing resistance to movement of the sheet S in the sheet width direction.

[0058] As shown in FIG. 4(e), in this embodiment, the second registration roller pair 244 is shifted so that the center Xs of the sheet S in the sheet width direction is aligned with the conveyance center X0. The conveyance center X0 is the reference for the sheet position in the sheet width direction. In addition, in the image forming unit 1B, a toner image is formed assuming that the center Xs of the sheet S is the conveyance center X0.

[0059] In the cardboard mode (first mode) of this embodiment, skew correction of the sheet S is not performed in the second registration roller pair 244. That is, in the cardboard mode (first mode), the leading edge of the sheet S passes through the second registration roller pair 244 without being abutted against the second registration roller pair 244 (third roller pair) that is in a stopped state.

[0060] After the second registration roller pair 244 is shifted, the sheet S is discharged from the sheet feeding device 2 (FIG. 1) as described above, and an image is formed on the sheet S in the image forming apparatus main body 1A.

[0061] Here, when correcting skew of a highly rigid sheet S, it is preferable to form a loop L of the sheet S in the section where the curve angle of the conveying path is large, from the upper conveying roller pair 245 to the first registration roller pair 243. This can reduce the possibility of the leading edge of the sheet S penetrating through the nip portion N2 of the first registration roller pair 243 or of poor skew correction due to slippage of the upper conveying roller pair 245.

[0062] Specifically, the bending of the sheet S along the conveying path and the formation of the loop L during skew correction generate a force (bending stress) in the sheet S that tends to stretch it into a flat shape. This force acts on the leading edge of the sheet S as a thrust force directed downstream in the sheet conveying direction and a force directed outward from the curvature of the sheet S in the thickness direction of the sheet S. Furthermore, this force acts on the trailing edge of the sheet S as a thrust force directed upstream in the sheet conveying direction and a force directed outward from the curvature of the sheet S in the thickness direction of the sheet S.

[0063] The force that stretches the sheet S into a flat shape becomes stronger as the rigidity of the sheet S increases. Therefore, when correcting skew of a highly rigid sheet S, there is a concern that the corner on the leading edge of the sheet S on the leading side may penetrate through the nip portion N2 of the first registration roller pair 243 due to the force in the thrust direction, resulting in improper skew correction. Furthermore, if the upper conveying roller pair 245, which is required to push the sheet S toward the first registration roller pair 243 while forming the loop L, slips relative to the sheet S due to the force in the thrust direction, the loop L will not be formed sufficiently. As a result, there is a concern that improper skew correction will occur.

[0064] On the other hand, the relationship between the thrust force component and the thickness force component acting on the leading or trailing end of the sheet S varies depending on the degree of curvature of the sheet S. In other words, when the sheet S is significantly curved, the thickness force component of the force acting on the leading or trailing end of the sheet S due to the force that tries to stretch the sheet S into a flat shape becomes larger, and the thrust force component of the sheet S becomes relatively smaller.

[0065] In this embodiment, the highly rigid sheet S is subjected to skew correction while being significantly curved between the upper conveying roller pair 245 and the first registration roller pair 243. Therefore, the thrust force applied to the leading edge of the sheet S during skew correction is relatively small. As a result, it is possible to prevent the occurrence of h, which occurs when the leading edge corner of the sheet penetrates through the nip portion N2 of the first registration roller pair 243. In addition, the thrust force applied to the trailing edge of the sheet S during skew correction is also relatively small. As a result, it is possible to prevent poor skew correction caused by the upper conveying roller pair 245 slipping relative to the sheet S.

[0066] (Thin paper mode) Figures 5(a) to 5(e) are diagrams showing the correction operation of the registration unit 240 in the thin paper mode. The order of Figures 5(a) to 5(d) is the same as the chronological order of the correction operation. Figure 5(e) is a schematic diagram of the registration unit 240 seen from above at the same time as Figure 5(d).

[0067] 5A, in the thin paper mode (second mode) of this embodiment, skew correction of the sheet S is not performed in the first registration roller pair 243. That is, in the thin paper mode (second mode), the leading edge of the sheet S passes through the first registration roller pair 243 without being abutted against the stopped first registration roller pair 243 (second roller pair).

[0068] 5A, the sheet S is conveyed from the first pair of registration rollers 243 to the second pair of registration rollers 244. At this point, the second pair of registration rollers 244 is not rotated and is in a stopped state. The stopped state of the second pair of registration rollers 244 is maintained until a predetermined time has elapsed even after the leading edge of the sheet S is detected by the second conveyance sensor S2.

[0069] While the second registration roller pair 244 is stopped, the leading edge of the sheet S abuts against the nip portion N3 of the second registration roller pair 244, and even after the abutment, the first registration roller pair 243 continues to convey the sheet S. As a result, as shown in FIG. 5B, a flexure (loop L) of the sheet S is formed between the first registration roller pair 243 and the second registration roller pair 244. At this time, the formation of the loop L is permitted by the space γ1 on the side of the upper guide 304a of the horizontal path γ described above.

[0070] When a loop L is formed in the sheet S, stress is generated in the sheet S to resolve the loop L. This stress causes the leading edge of the sheet S to pivot so as to follow the nip portion N3 of the second registration roller pair 244. In other words, if the sheet S is skewed, one of the two corners of the leading edge of the sheet S (the leading side) reaches the nip portion N3 earlier than the other (the lagging side). Thereafter, as the loop L is formed, the leading edge of the sheet S pivots so that the corner on the lagging side moves downstream in the sheet conveyance direction, with the corner on the leading side as a fulcrum, and the skew of the sheet S is corrected.

[0071] 5C, the second pair of registration rollers 244 starts to rotate, and the second pair of registration rollers 244 starts to convey the sheet S. After the second pair of registration rollers 244 starts to be driven, the nip portions N1 and N2 between the upper pair of conveying rollers 245 and the first pair of registration rollers 243 are released. By releasing the nip portions N1 and N2, it is possible to prevent an increase in conveyance resistance caused by the loop L of the sheet S rubbing against the upper guide 304a.

[0072] After the second pair of registration rollers 244 starts conveying the sheet S, the position of the sheet edge in the sheet width direction is detected by the lateral registration sensor S3 (FIG. 5(d)). Then, as shown in FIG. 5(e), based on the detection result of the lateral registration sensor S3, while the second pair of registration rollers 244 is nipping and conveying the sheet S, the second pair of registration rollers 244 is shifted in the sheet width direction. While the second pair of registration rollers 244 is shifted, the nip portions N2 and N1 of the first pair of registration rollers 243 and the upper conveyance roller pair 245, which are upstream of the second pair of registration rollers 244, are maintained in an open state. This reduces resistance to the movement of the sheet S in the sheet width direction.

[0073] Here, when correcting skew of a sheet S having low rigidity, it is preferable to form a loop L of the sheet S in the section where the curve angle of the conveying path is small, from the first pair of registration rollers 243 to the second pair of registration rollers 244. This reduces the possibility of poor skew correction due to insufficient rotation of the leading edge of the sheet S.

[0074] Specifically, the force that stretches the sheet S into a flat shape becomes weaker as the rigidity of the sheet S decreases. Therefore, when correcting skew of a sheet S with low rigidity, even when the loop L is formed, the thrust force applied to the leading edge of the sheet is insufficient, and the corner on the lagging side cannot catch up with the corner on the leading side, which raises concerns about poor skew correction.

[0075] On the other hand, for the reasons mentioned above, when the curvature of the sheet S is small, the thrust force component of the force acting on the leading and trailing ends of the sheet S due to the force that causes the sheet S to stretch flat becomes larger, and the force component in the thickness direction of the sheet S becomes relatively smaller.

[0076] In this embodiment, the sheet S, which has low rigidity, is skew-corrected by forming a loop in the substantially linear horizontal path γ between the first registration roller pair 243 and the second registration roller pair 244. Therefore, a relatively large thrust force is applied to the leading edge of the sheet S during skew correction. As a result, the leading edge of the sheet can be rotated so that the corner on the lagging side of the leading edge of the sheet catches up with the corner on the leading edge, thereby suppressing poor skew correction.

[0077] <Control configuration> 7 is a block diagram showing the control configuration of the image forming apparatus 1 in this embodiment. Each element in FIG. 7 except for the computer 204 may be mounted in the image forming apparatus main body 1A or the sheet feeding device 2.

[0078] The image forming apparatus 1 includes a control unit 200 as a control means for controlling the overall operation of the image forming apparatus 1, and various motors (M1 to M3) and various sensors (S1 to S3) connected to the control unit 200. The control unit 200 functions as a control means for controlling the operation of the register unit 240.

[0079] The control unit 200 includes a CPU 201, a memory 202, an operation unit 203, an image formation control unit 205, a sheet conveyance control unit 206, a sensor control unit 207, and a shift control unit 208. The image formation control unit 205, the sheet conveyance control unit 206, the sensor control unit 207, and the shift control unit 208 are function achieving means provided in the control unit 200. These function achieving means may be arranged as a dedicated processor (such as an ASIC) independent of the CPU 201, or may be implemented in software as part of a program executed by the CPU 201.

[0080] The CPU 201 reads and executes a program stored in the memory 202 as a storage unit, and issues instructions to each function achieving means to execute a print job in accordance with a flowchart (FIG. 6) described later. The CPU 201 is also connected to a computer 204 external to the image forming apparatus 1 via an external interface and a network so as to be able to communicate with the computer 204.

[0081] The operation unit 203 is a user interface for the image forming apparatus 1 and includes an input unit that receives setting information and operational instructions for the image forming apparatus 1 from the user, and a display unit that displays information to the user. The image formation control unit 205 controls the operation of the image forming unit 1B. The image formation control unit 205 controls the operation of the exposure / writing unit that drives the exposure device 511 based on image information received by the CPU 201 from the computer 204, for example. The sheet conveyance control unit 206 controls the drive of the conveyance motor M1 and the separation motor M2. As described above, the registration unit 240 in this embodiment is driven by multiple conveyance motors M1 and multiple separation motors M2. The sensor control unit 207 receives signals from various sensors, including the first conveyance sensor S1 and the second conveyance sensor S2. The shift control unit 208 receives the detection result of the lateral registration sensor S3 and controls the drive of the shift motor M3.

[0082] <Print job flow> Next, the procedure by which the control unit 200 of this embodiment executes a print job will be described with reference to the flowchart of FIG. 6, focusing mainly on the correction operation in the registration unit 240.

[0083] The control unit 200 starts a print job when it receives a print execution instruction from a user, for example, from an external computer 204 (S101). A print job is a series of tasks that execute image formation operations based on instructions from the user. The print job includes the number of copies and sheets to be printed, attribute information of the sheets S to be used for printing, and the like, which are set by the user. The attribute information of the sheets S includes information on the basis weight and size of the sheets S, the brand of the sheets S, and the like.

[0084] When the control unit 200 starts a print job, it causes the sheet feeding device 2 (or the main body feeding unit 51) to start feeding the sheet S (S102). The control unit 200 analyzes the attribute information of the sheet S acquired when the print job is accepted, and determines whether to apply the thick paper mode or the thin paper mode (S103). As an example, in this embodiment, the basis weight of the sheet S is set to 151 g / m 2 In the above cases, apply the thick paper mode and use a paper weight of 150 g / m 2 The thin paper mode is applied in the following cases: However, the basis weight threshold can be changed, and attribute information other than basis weight (for example, whether or not the paper is surface treated) can be taken into consideration to determine whether the paper mode is thick or thin.

[0085] In the case of the cardboard mode (S103 YES), as described above, the control unit 200 causes the leading edge of the sheet S to abut against the stopped first registration roller pair 243 to form a loop L (S104). When a predetermined time T1 has elapsed since the first conveyance sensor S1 detected the leading edge, the control unit 200 causes the first registration roller pair 243 to start conveying the sheet S (S105). When a predetermined standby time has elapsed since the first registration roller pair 243 started conveying, the control unit 200 separates the roller pair (245) upstream of the first registration roller pair 243 (S106). The roller pair separated in S106 is brought into contact again before the leading edge of the succeeding sheet arrives.

[0086] Next, the control unit 200 causes the sheet S to pass through the nip portion N3 of the second registration roller pair 244 without performing skew correction again by the second registration roller pair 244, and causes the second registration roller pair 244 to convey the sheet S (S107). When a predetermined waiting time has elapsed since the leading edge of the sheet S reached the nip portion N3 of the second registration roller pair 244, the control unit 200 separates the roller pair (243) upstream of the second registration roller pair 244 (S108). The roller pair separated in S108 is brought into contact with each other again before the leading edge of the succeeding sheet arrives.

[0087] After separating the upstream roller pair in S108, the control unit 200 shifts the second registration roller pair 244 based on the detection result of the lateral registration sensor S3 while continuing to convey the sheet S by the second registration roller pair 244 (S109). Then, the control unit 200 discharges the sheet S from the sheet feeding device 2 to the image forming apparatus main body 1A.

[0088] Thereafter, the control unit 200 performs final skew correction and horizontal registration on the sheet S in the skew correction unit 55 (FIG. 1) of the image forming apparatus main body 1A (S115), and then causes the secondary transfer unit of the image forming unit 1B to transfer the image onto the sheet S (S116). Furthermore, the control unit 200 causes the fixing device 58 to fix the image on the sheet S (S118), and then reverses and discharges the sheet S depending on whether double-sided printing is performed or whether face-down printing is performed (S119). If there is a subsequent sheet S on which an image is to be formed (S119 YES), the control unit 200 returns to S103 and continues processing. If there is no subsequent sheet S (S119 NO), the control unit 200 ends the print job (S120).

[0089] On the other hand, in the thin paper mode (S103NO), as described above, the control unit 200 causes the sheet S to pass through the nip portion N2 of the first registration roller pair 243 without correcting skew at the first registration roller pair 243, and causes the first registration roller pair 243 to convey the sheet S (S110). Thereafter, the control unit 200 causes the leading edge of the sheet S to abut against the second registration roller pair 244, which is in a stopped state, to form a loop L (S111).

[0090] When a predetermined time T2 has elapsed since the second conveyance sensor S2 detected the leading edge, the control unit 200 starts conveying the sheet S by the second registration roller pair 244 (S112). When a predetermined standby time has elapsed since the second registration roller pair 244 started conveying, the control unit 200 separates the roller pair (245, 243) upstream of the second registration roller pair 244 (S113). The roller pair separated at 113 is brought into contact with each other again before the leading edge of the succeeding sheet arrives.

[0091] After separating the upstream roller pair in S113, the control unit 200 shifts the second registration roller pair 244 based on the detection result of the lateral registration sensor S3 while continuing to convey the sheet S by the second registration roller pair 244 (S114). Then, the control unit 200 discharges the sheet S from the sheet feeding device 2 to the image forming apparatus main body 1A. The subsequent print job processing (S115 to S120) is the same as in the thick paper mode, and therefore will not be described here.

[0092] <Summary of this Example> In this embodiment, the angle θ1 between the nip line direction D1 of the upper conveying roller pair 245 and the nip line direction D2 of the first registration roller pair 243 is larger than the angle θ2 between the nip line direction D2 of the first registration roller pair 243 and the nip line direction D3 of the second registration roller pair 244. In other words, the movement direction of the sheet at the nip portion N1 of the upper conveying roller pair 245 (first roller pair) is defined as the first direction (D1). The movement direction of the sheet at the nip portion N2 of the first registration roller pair 243 (second roller pair) is defined as the second direction (D2). The movement direction of the sheet at the nip portion N3 of the second registration roller pair 244 (third roller pair) is defined as the third direction (D3). In this case, the angle θ1 between the first direction (D1) and the second direction (D2) is larger than the angle θ2 between the second direction and the third direction (θ1>θ2).

[0093] The control unit 200 of this embodiment can execute a thick paper mode (first mode) and a thin paper mode (second mode) by operating the registration unit 240. In the thick paper mode, the leading edge of the sheet is abutted against the first registration roller pair 243 (second roller pair) in a stopped state to correct the skew of the sheet, and then the leading edge of the sheet passes through the second registration roller pair 244 (third roller pair) without abutting against the second registration roller pair 244 (third roller pair) in a stopped state. In the thin paper mode, the leading edge of the sheet is abutted against the second registration roller pair 244 (third roller pair) in a stopped state to correct the skew of the sheet.

[0094] The control unit 200 of this embodiment executes a thick paper mode (first mode) when conveying a sheet having a first basis weight, and executes a thin paper mode (second mode) when conveying a sheet having a second basis weight smaller than the first basis weight. The first basis weight is, for example, a basis weight of 151 g / m 2 More than 190g / m 2 The second basis weight is, for example, 150 g / m 2 Less than 60g / m 2 The first basis weight is 500 g / m 2 The second basis weight may be 52 g / m or more. 2 The following ultra-thin paper may also be used.

[0095] According to the above configuration, in the thick paper mode, a loop is formed in a conveying path where the angle θ1 between the nip line directions D1 and D2 is large, while the first registration roller pair 243 performs skew correction of the sheet. Therefore, as described above, it is possible to reduce the possibility of improper skew correction due to the leading edge penetrating through the nip portion N2 of the first registration roller pair 243 or due to slippage of the upper conveying roller pair 245. Furthermore, in the thin paper mode, a loop is formed in a conveying path where the angle θ2 between the nip line directions D2 and D3 is small, while the second registration roller pair 244 performs skew correction of the sheet. Therefore, it is possible to reduce the possibility of improper skew correction due to insufficient force in the thrust direction to rotate the leading edge of the sheet S when the loop is formed.

[0096] That is, according to this embodiment, it is possible to provide a sheet conveying device and an image forming apparatus that can achieve higher skew correction accuracy mainly for a variety of sheets having different basis weights.

[0097] In this embodiment, the upper conveying path α (sheet conveying path) formed by the upper guide 301a (first guide) and the lower guide 301b (second guide) is curved so that the lower guide 301b (second guide) is on the outside of the curve. Furthermore, the upper guide 301a (first guide) and the lower guide 301b (second guide) are configured to allow the sheet S to bend toward the outside of the curve of the upper conveying path α when correcting skew of the sheet S in the thick paper mode (first mode).

[0098] This allows skew correction in the thick paper mode to be performed with the sheet S curved significantly along the curved upper conveying path α. As a result, the possibility of improper skew correction due to the leading edge of the sheet S penetrating through the first registration roller pair 243 or slippage of the upper conveying roller pair 245 can be more reliably reduced.

[0099] In this embodiment, the nip portion N2 of the first registration roller pair 243 (second roller pair) is disposed below the nip portion N1 of the upper conveying roller pair 245 (first roller pair). The nip line direction D1 (first direction) of the upper conveying roller pair 245 is a direction facing downward in the vertical direction and is closer to the vertical direction than the horizontal. On the other hand, the first registration roller pair 243 (second direction) is a direction closer to the horizontal direction than the vertical direction.

[0100] In this configuration, when a sheet S with low rigidity is abutted against the first registration roller pair 243 to attempt to correct skew, a portion of the sheet S may bend downward due to gravity even before the loop is formed. In this case, the amount of loop after abutting against the first registration roller pair 243 may be insufficient, resulting in improper skew correction. According to the configuration of this embodiment, skew correction is not performed on a sheet S with low rigidity by the first registration roller pair 243, so this kind of inconvenience can be avoided.

[0101] Furthermore, in this embodiment, the upper guide 304a (third guide) and the lower guide 304b (fourth guide) are configured to allow the sheet S to bend upward when correcting skew in the thin paper mode (second mode). That is, the space γ1 (FIG. 2) that accommodates the loop L of the sheet S in the thin paper mode is provided in the upper part of the horizontal path γ. Because thin paper (especially ultra-thin paper) has low rigidity, if the space γ1 that accommodates the loop L is provided in the lower part of the horizontal path γ, the sheet S may bend toward the space γ1 even before the loop is formed, which may result in poor skew correction. The configuration of this embodiment makes it possible to avoid such inconveniences.

[0102] In this embodiment, the angle θ3 between the nip line direction D4 of the lower conveying roller pair 246 and the nip line direction D2 of the first registration roller pair 243 is larger than the angle θ2 between the nip line direction D2 of the first registration roller pair 243 and the nip line direction D3 of the second registration roller pair 244. In other words, the movement direction of the sheet at the nip portion N4 of the lower conveying roller pair 246 (fourth roller pair) is defined as the fourth direction (D4). In this case, the angle θ3 between the fourth direction (D4) and the second direction (D2) is larger than the angle θ2 between the second direction and the third direction (θ3>θ2). The control unit 200 executes the thick paper mode (first mode) when a sheet with a large basis weight is conveyed via the lower conveying path β (second conveying path), and executes the thin paper mode (second mode) when a sheet with a small basis weight is conveyed via the lower conveying path β (second conveying path).

[0103] This makes it possible to accommodate a variety of sheet materials by transporting the sheet through a plurality of transport paths, and to achieve higher skew correction accuracy for a variety of sheets.

[0104] In this embodiment, the magnitude relationship between the angles θ1 and θ3 is θ1 > θ3. That is, the curve angle of the upper conveying path α between the upper conveying roller pair 245 and the first registration roller pair 243 is greater than the curve angle of the lower conveying path β between the lower conveying roller pair 246 and the first registration roller pair 243. In this case, for example, the conveying distance from the lower conveying roller pair 246 to the first registration roller pair 243 may be longer than the conveying distance from the upper conveying roller pair 245 to the first registration roller pair 243. This makes it less likely for the leading edge of the cardboard to penetrate through the first registration roller pair 243 or for the upper conveying roller pair 245 to slip when conveying cardboard via the lower conveying path β. Note that the conveying distance is the distance measured along the conveying path from the nip portion of the upstream roller pair to the nip portion of the downstream roller pair. If the conveying path is curved, it is measured along the guides on the inside of the curve (upper guide 301a, lower guide 203b).

[0105] (Variation 1) In the above-described embodiment, a configuration in which angle θ1 is greater than angle θ2 has been described. This is not limiting, and the present technology may also be applied to a configuration in which angle θ1 is smaller than angle θ2, for example. In this modified example, the curvature angle (θ2) of the conveying path between the first pair of registration rollers 243 and the second pair of registration rollers is greater than the curvature angle (θ1) of the upstream upper conveying path α. In this case, a sheet S with low rigidity, such as thin paper, can be skew-corrected by the first pair of registration rollers 243 so as to form a loop on the upper conveying path α. Furthermore, a sheet S with high rigidity, such as thick paper, can be skew-corrected by the second pair of registration rollers 244 so as to form a loop on the conveying path between the first pair of registration rollers 243 and the second pair of registration rollers.

[0106] That is, in the thick paper mode (first mode) of this modified example, the leading edge of the sheet passes through the first registration roller pair 243 (second roller pair) without abutting against the first registration roller pair 243 (second roller pair) in a stopped state. Thereafter, the leading edge of the sheet is abutted against the second registration roller pair (third roller pair) in a stopped state to correct the skew of the sheet. In addition, in the thin paper mode (second mode) of this modified example, the leading edge of the sheet is abutted against the first registration roller pair 243 (second roller pair) in a stopped state to correct the skew of the sheet. Thereafter, the leading edge of the sheet passes through the second registration roller pair 244 (third roller pair) without abutting against the second registration roller pair 244 (third roller pair) in a stopped state. The control unit 200 executes the thick paper mode (first mode) when conveying a sheet having a first basis weight, and executes the thin paper mode (second mode) when conveying a sheet having a second basis weight smaller than the first basis weight.

[0107] As a result, similar to the above-described embodiment, it is possible to provide a sheet conveying device and an image forming apparatus that can achieve higher skew correction accuracy for a variety of sheets.

[0108] (Variation 2) In the above-described embodiment, the thick paper mode and thin paper mode are determined based on basis weight. However, the thick paper mode and thin paper mode may be determined based on criteria other than basis weight. For example, the thick paper mode may be applied to coated paper with a resin layer formed on its surface, regardless of basis weight. Furthermore, recycled paper may have lower rigidity than plain paper even if it has the same basis weight, so the thin paper mode may be applied to recycled paper. Furthermore, the thick paper mode / thin paper mode settings for combinations of basis weight information and information other than basis weight may be determined in advance and stored in the memory 202 of the control unit 200 in the form of a table or the like. The thick paper mode / thin paper mode may be determined by referring to the information when a print job is executed.

[0109] Even when selecting the thick paper mode or the thin paper mode based on criteria different from those in the embodiment, the control unit 200 executes the thick paper mode (first mode) for a first sheet having high rigidity and executes the thin paper mode (second mode) for a second sheet having low rigidity. This makes it possible to provide a sheet conveying device and an image forming device that can achieve higher skew correction accuracy for a variety of sheets, regardless of the basis weight.

[0110] (Other variations) In the above-described embodiment, a configuration in which one of two modes (thick paper mode and thin paper mode) is applied has been described. However, the control unit 200 may also be capable of executing another mode (third mode) different from either the thick paper mode or the thin paper mode. The other mode may be, for example, a mode in which the leading edge of the sheet is abutted against the first registration roller pair 243, which is in a stopped state, to perform a first skew correction, and then the leading edge of the sheet is abutted against the second registration roller pair 244, which is also in a stopped state, to perform a second skew correction. This mode further improves the accuracy of skew correction by performing skew correction multiple times. The other mode may also be, for example, a mode in which skew correction is not performed by either the first registration roller pair 243 or the second registration roller pair 244, and prioritizes rapid sheet conveyance.

[0111] (Other embodiments) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions. [Explanation of symbols]

[0112] 200...control unit / 243...second roller pair (first registration roller pair) / 244...third roller pair (second registration roller pair) / 245...first roller pair (upper conveying roller pair) / 246...fourth roller pair (lower conveying roller pair) / D1...first direction (nip line direction) / D2...second direction (nip line direction) / D3...third direction (nip line direction) / D4...fourth direction (nip line direction)

Claims

1. a first roller pair for conveying a sheet; a second roller pair disposed downstream of the first roller pair in a sheet transport path and configured to transport the sheet; a third roller pair disposed downstream of the second roller pair in the conveying path and configured to convey a sheet; A control unit; Equipped with When the moving direction of the sheet in the nip portion of the first roller pair is defined as a first direction, the moving direction of the sheet in the nip portion of the second roller pair is defined as a second direction, and the moving direction of the sheet in the nip portion of the third roller pair is defined as a third direction, an angle between the first direction and the second direction is larger than an angle between the second direction and the third direction, the control unit is capable of executing a first mode in which a leading edge of the sheet is abutted against the second roller pair in a stopped state to correct skew of the sheet, and then the leading edge of the sheet passes through the third roller pair in a stopped state without abutting against the third roller pair in a stopped state, and a second mode in which a leading edge of the sheet is abutted against the third roller pair in a stopped state to correct skew of the sheet, and then the leading edge of the sheet passes through the second roller pair in a stopped state without abutting against the second roller pair in a stopped state, the control unit executes the first mode when conveying a sheet having a first basis weight, and executes the second mode when conveying a sheet having a second basis weight smaller than the first basis weight. A sheet conveying device characterized by:

2. The first guide, a second guide that, together with the first guide, forms a sheet conveying path between the first roller pair and the second roller pair; Further provided with the sheet transport path is curved so that the second guide is on the outside of the curve, the first guide and the second guide are configured to allow the sheet to bend toward the outside of the curvature when correcting skew of the sheet in the first mode.

2. The sheet transport device according to claim 1.

3. The third guide, a fourth guide disposed below the third guide and forming a sheet conveying path between the second roller pair and the third roller pair together with the third guide; Further provided with The third guide forms a space that allows the sheet to bend upward when correcting skew of the sheet in the second mode.

3. The sheet transport device according to claim 2.

4. a nip portion of the second roller pair is disposed below a nip portion of the first roller pair, the first direction is a direction facing downward in a vertical direction and is closer to the vertical direction than to a horizontal direction, The second direction is closer to horizontal than the vertical direction.

3. The sheet transport device according to claim 2.

5. The third guide, a fourth guide disposed below the third guide and forming a sheet conveying path between the second roller pair and the third roller pair together with the third guide; Further provided with the third guide forms a space that allows the sheet to bend upward when correcting skew of the sheet in the second mode.

2. The sheet transport device according to claim 1.

6. the conveying path is a first conveying path, and a fourth roller pair is disposed on a second conveying path that merges with the first conveying path and conveys a sheet toward the second roller pair; When a moving direction of the sheet in the nip portion of the fourth roller pair is defined as a fourth direction, an angle between the fourth direction and the second direction is larger than an angle between the second direction and the third direction, the control unit executes the first mode when a sheet having the first basis weight is transported via the second transport path, and executes the second mode when a sheet having the second basis weight is transported via the second transport path.

2. The sheet transport device according to claim 1.

7. a position detection unit that detects an edge position of the sheet in a sheet width direction parallel to a rotation axis of the third roller pair; a moving means for moving the third roller pair in the sheet width direction based on a detection result of the position detection unit; Further comprising:

2. The sheet transport device according to claim 1.

8. a first roller pair for conveying a sheet; a second roller pair disposed downstream of the first roller pair in a sheet transport path and configured to transport the sheet; a third roller pair disposed downstream of the second roller pair in the conveying path and configured to convey a sheet; A control unit; Equipped with When the moving direction of the sheet in the nip portion of the first roller pair is defined as a first direction, the moving direction of the sheet in the nip portion of the second roller pair is defined as a second direction, and the moving direction of the sheet in the nip portion of the third roller pair is defined as a third direction, an angle between the first direction and the second direction is smaller than an angle between the second direction and the third direction, the control unit is capable of executing a first mode in which the leading edge of the sheet passes through the second pair of rollers without abutting against the second pair of rollers in a stopped state, and then abuts the leading edge of the sheet against the third pair of rollers in a stopped state to correct skew of the sheet; and a second mode in which the leading edge of the sheet abuts against the second pair of rollers in a stopped state to correct skew of the sheet, and then abuts the leading edge of the sheet against the third pair of rollers in a stopped state, and then abuts the leading edge of the sheet against the third pair of rollers in a stopped state, the control unit executes the first mode when conveying a sheet having a first basis weight, and executes the second mode when conveying a sheet having a second basis weight smaller than the first basis weight. A sheet conveying device characterized by:

9. a first roller pair for conveying a sheet; a second roller pair disposed downstream of the first roller pair in a sheet transport path and configured to transport the sheet; a third roller pair disposed downstream of the second roller pair in the conveying path and configured to convey a sheet; A control unit; Equipped with When the moving direction of the sheet in the nip portion of the first roller pair is defined as a first direction, the moving direction of the sheet in the nip portion of the second roller pair is defined as a second direction, and the moving direction of the sheet in the nip portion of the third roller pair is defined as a third direction, an angle between the first direction and the second direction is larger than an angle between the second direction and the third direction, the control unit is capable of executing a first mode in which a leading edge of the sheet is abutted against the second roller pair in a stopped state to correct skew of the sheet, and then the leading edge of the sheet passes through the third roller pair in a stopped state without abutting against the third roller pair in a stopped state, and a second mode in which a leading edge of the sheet is abutted against the third roller pair in a stopped state to correct skew of the sheet, and then the leading edge of the sheet passes through the second roller pair in a stopped state without abutting against the second roller pair in a stopped state, the control unit executes the first mode when conveying a first sheet, and executes the second mode when conveying a second sheet having a lower rigidity than the first sheet. A sheet conveying device characterized by:

10. The sheet conveying device according to any one of claims 1 to 9; an image forming means for forming an image on the sheet conveyed by the sheet conveying device; An image forming apparatus comprising:

Images