CN117492339A - Sheet conveying apparatus and image forming apparatus - Google Patents

Abstract

The present disclosure relates to a sheet conveying apparatus and an image forming apparatus. The sheet conveying apparatus includes a first skew correction portion, a second skew correction portion, an acquisition unit, and a control unit. The first skew correction portion corrects skew of the sheet by abutting a leading edge of the sheet against the first roller pair to form a bend in the sheet. The second skew correction portion corrects skew of the sheet by conveying the sheet in a steering motion. When a first sheet having a first length is conveyed, the control unit corrects skew of the first sheet by the second skew correction portion. When a second sheet having a second length longer than the first length is conveyed, the control unit corrects the skew of the second sheet by the first skew correction portion, and is configured not to correct the skew of the second sheet by the second skew correction portion.

Description

Sheet conveying apparatus and image forming apparatus

Technical Field

The present disclosure relates to a sheet conveying apparatus that conveys a sheet in a copying machine, a facsimile machine, and a multifunction machine including a plurality of these functions, and an image forming apparatus that forms an image on a sheet conveyed by the sheet conveying apparatus.

Background

Heretofore, in the field of commercial printing in which deliverables output from an image forming apparatus are sold as commercial products, there has been a demand for an image forming apparatus having medium scalability and high productivity. In particular, to accommodate a wide variety of deliverables, it is desirable to pass a medium called a strip of paper (long sheet) that exceeds a standard size of up to about 19 inches, for example. As a registration mechanism that ensures high productivity and high quality, an inclined conveyance registration unit (hereinafter referred to as inclined conveyance registration) is known (see japanese patent laid-open No. 2021-134050). The oblique conveying registration can highly accurately correct the posture of the sheet by conveying the sheet obliquely using an oblique conveying roller and then bringing the sheet against the contact surface. According to this configuration, since correction can be performed while conveying the sheet, an image can be formed without reducing productivity.

However, with the configuration described in japanese patent laid-open No.2021-134050, in operating the inclined conveyance registration, if the sheet is conveyed obliquely, and the trailing edge of the sheet is nipped by the conveyance roller pair disposed upstream of the inclined conveyance roller in the sheet conveyance direction, the sheet may twist and stress may be generated. If such stress occurs, image defects may occur due to occurrence of such as wrinkles, folds, and skew in the sheet. Therefore, in the case of conveying a sheet by the inclined conveying roller, it is desirable to release the nip by separating a plurality of conveying roller pairs arranged upstream of the inclined conveying roller in the sheet conveying direction. However, in the case where all of a plurality of these conveying roller pairs are provided with a separate driving configuration, an increase in the number of parts may result in an increase in cost, an increase in equipment, and an increase in process complexity. Further, since the long sheet is long in the sheet length, in the case where the sheet is nipped and conveyed only by the inclined conveying roller, resistance to which the sheet is subjected from the conveying guide becomes large, and wrinkles and skew may occur.

An object of the present disclosure is to provide a sheet conveying apparatus and an image forming apparatus, which can highly accurately correct skew of a sheet while suppressing an increase in the size and cost of the apparatus.

Disclosure of Invention

According to a first aspect of the present invention, a sheet conveying apparatus includes: a first skew correction portion including a first roller pair configured to convey a sheet and a second roller pair disposed upstream of the first roller pair in a sheet conveying direction and configured to convey the sheet, the first skew correction portion being configured to correct skew of the sheet conveyed by the second roller pair by abutting a leading edge of the sheet against the first roller pair to form a bend in the sheet; a second skew correction portion including a pair of steering rollers configured to convey a sheet, the second skew correction portion being configured to correct skew of the sheet by conveying the sheet in a steering motion using the pair of steering rollers; an acquisition unit configured to acquire information about a sheet length; and a control unit configured to control the first skew correction portion and the second skew correction portion based on the information on the sheet length acquired by the acquisition unit. In the case of conveying a first sheet of a first length, the control unit is configured to correct skew of the first sheet by the second skew correction portion. In the case of conveying a second sheet of a second length longer than the first length, the control unit is configured to correct skew of the second sheet by the first skew correction portion, and is configured not to correct skew of the second sheet by the second skew correction portion.

According to a second aspect of the present invention, an image forming apparatus includes the sheet conveying apparatus and an image forming unit configured to form an image on a sheet conveyed by the sheet conveying apparatus.

Other features of the present invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings.

Drawings

Fig. 1 is a sectional view showing an image forming apparatus of the present embodiment.

Fig. 2 is a block diagram showing a control system of the image forming apparatus of the embodiment.

Fig. 3 is a perspective view showing the registration unit of this embodiment.

Fig. 4 is a plan view showing the registration unit of this embodiment.

Fig. 5 is a sectional view showing the registration unit of this embodiment.

Fig. 6A is a plan view showing a state in which the leading edge of the short sheet has reached the second skew correction portion in the registration unit of the embodiment.

Fig. 6B is a plan view showing a state in which skew of an inexpensive sheet has been corrected by the second skew correction portion in the registration unit of the embodiment.

Fig. 7A is a plan view showing a state in which the leading edge of the short sheet is nipped by the registration roller pair in the registration unit of the embodiment.

Fig. 7B is a plan view showing a state in which the leading edge of the short sheet reaches the secondary transfer nip portion of the embodiment.

Fig. 8A is a plan view showing a state immediately before the leading edge of the long sheet reaches the pre-registration roller pair in the registration unit of the embodiment.

Fig. 8B is a sectional view showing a state immediately before the leading edge of the long sheet reaches the pre-registration roller pair in the registration unit of the embodiment.

Fig. 9A is a plan view showing a state in which the leading edge of the long sheet has reached the pair of rollers before registration and has formed a loop in the registration unit of the embodiment.

Fig. 9B is a sectional view showing a state in which the leading edge of the long sheet has reached the pair of rollers before registration and has formed a loop in the registration unit of the embodiment.

Fig. 10A is a plan view showing a state immediately before the leading edge of the long sheet reaches the secondary transfer nip portion of the embodiment.

Fig. 10B is a sectional view showing a state immediately before the leading edge of the long sheet reaches the secondary transfer nip portion of the embodiment.

Fig. 11 is a flowchart showing processing steps performed by the registration unit of the embodiment when conveying a sheet.

Fig. 12 is a plan view showing a state in which the second skew correction portion performs skew correction on a long sheet.

Fig. 13 is a plan view showing a case of the registration unit in which a registration method based on a velocity difference is used as the second skew correction section.

Fig. 14 is a plan view showing a case of the registration unit in which a registration method based on a wobble shift is used as the second skew correction section.

Detailed Description

Hereinafter, the present embodiment will be described using the drawings. First, a schematic configuration of the image forming apparatus of the present embodiment will be described using fig. 1. Fig. 1 is a sectional view showing an image forming apparatus of the present embodiment.

Schematic construction of image forming apparatus

The printer 1 serving as an image forming apparatus is a full-color laser beam printer of an electrophotographic system. As shown in fig. 1, the printer 1 includes a casing 1a and a casing 1b, the casing 1a including a unit that performs sheet feeding and image forming, and the casing 1b including a unit that performs fixing and cooling.

The casing 1a includes sheet feeding units 10a, 10b, and 10c, extracting units 20a and 20b, a registration unit (hereinafter referred to as a registration unit 3), an image forming unit 40 serving as an image forming unit, and a first duplex conveying path 6. The casing 1b includes a fixing unit 100, a cooling unit 110, a branch conveying unit 120, a reverse conveying unit 130, a second duplex conveying unit 140, and a sheet discharging finisher unit 150.

The image forming unit 40 includes four process cartridges 40Y, 40M, 40C, and 40K, and exposure units 43Y, 43M, 43C, and 43K, which form toner images of 4 colors, that is, yellow (Y), magenta (M), cyan (C), and black (K), respectively. Note that the four process cartridges 40Y, 40M, 40C, and 40K are identical in configuration except for the colors of the images formed. Therefore, only the configuration and the image forming process of the process cartridge 40Y will be described, and the description of the process cartridges 40M, 40C, 40K will be omitted here.

The process cartridge 40Y includes a photosensitive drum 41, a charging roller (not shown), a developing unit 42, and a cleaner 45. The photosensitive drum 41 is constructed by coating the outer circumference of an aluminum cylinder with an organic photoconductive layer, and is rotatably driven by a driving motor (not shown). Further, an intermediate transfer belt 50 rotatably driven by a driving roller 52 in the arrow T direction is provided to the image forming unit 40, and the intermediate transfer belt 50 is wound around a stretching roller 51, the driving roller 52, and a secondary transfer inner roller 53. Primary transfer rollers 55Y, 55M, 55C, 55K are provided on the inner side of the intermediate transfer belt 50, and a secondary transfer outer roller 54 serving as a transfer roller facing the secondary transfer inner roller 53 is provided on the outer side of the intermediate transfer belt 50. The intermediate transfer belt 50 is an example of an image bearing member that bears a toner image.

The sheet feeding unit 10a includes a lifting plate 11a that rises and falls while stacking sheets S, a pickup roller 12a that feeds the sheets S stacked on the lifting plate 11a, and a separation roller pair 13a that separates the fed sheets one by one. Similarly, the sheet feeding unit 10b includes a lifting plate 11b that rises and falls while stacking the sheets S, a pickup roller 12b that feeds the sheets S stacked on the lifting plate 11b, and a separation roller pair 13b that separates the fed sheets one by one.

The sheet feeding unit 10c includes a loading tray 11c capable of loading sheets S, a separation roller pair 13c that feeds the sheets S loaded on the loading tray 11c while separating the sheets one by one, and a side edge regulating plate 14c. The side edge regulating plate 14c regulates the position of the side edge of the sheet S loaded on the loading tray 11 c. The sheet feeding units 10a and 10b are drawably provided inside the casing 1a, and are specifically capable of storing standard-sized sheets S. On the other hand, the sheet feeding unit 10c is pivotably provided on a side surface of the casing 1a, and can be opened and closed between an open position where the sheets S can be loaded and a closed position stored in the casing 1a along the side surface. The sheet feeding unit 10c can feed a cardboard having a large grammage sheet S, and a long sheet longer than a standard-sized sheet length in the sheet conveying direction. Hereinafter, using a case of feeding the sheet S from the sheet feeding unit 10c as an example, the present embodiment will be described.

The registration unit 3 includes a first skew correction portion 30 and a second skew correction portion 60, the second skew correction portion 60 being disposed downstream of the first skew correction portion 30 in the sheet conveying direction, the registration unit 3 being an example of a sheet conveying apparatus. On the other hand, the fixing unit 100 disposed in the casing 1b includes a pair of fixing rollers 101 capable of heating. Further, the cooling unit 110 includes an upper cooling belt 111a rotatably driven in the arrow T' direction by an upper cooling driving roller 112 a. Similarly, the cooling unit 110 includes a lower cooling belt 111b rotationally driven in the arrow T' direction by a lower cooling drive roller 112 b. Further, in order to cool the sheet, the cooling unit 110 includes a heat sink 113.

Imaging operation

Next, an image forming operation of the printer 1 configured as described above will be described. For example, when an image signal is input to the exposure unit 43 from a computer 300 (see fig. 2) such as an external personal computer, a laser beam corresponding to the image signal is emitted from the exposure unit 43 onto the photosensitive drum 41 of the process cartridge 40Y.

At this time, the surface of the photosensitive drum 41 has been uniformly charged to a predetermined polarity and potential by a charging roller (not shown) in advance, and irradiated with a laser beam from the exposure unit 43 via the mirror 44, forming an electrostatic latent image on the surface. The electrostatic latent image formed on the photosensitive drum 41 is developed by the developing unit 42, and a toner image of yellow (Y) is formed on the photosensitive drum 41.

Similarly, laser beams are also emitted from the exposure units 43M, 43C, and 43K onto each of the photosensitive drums of the process cartridges 40M, 40C, and 40K, and toner images of magenta (M), cyan (C), and black (K) are formed on the respective photosensitive drums. The primary transfer rollers 55Y, 55M, 55C, and 55K transfer the toner image of each color formed on each photosensitive drum onto the intermediate transfer belt 50. Then, the full-color toner image is conveyed to a secondary transfer nip T2 formed by a secondary transfer inner roller 53 and a secondary transfer outer roller 54 by an intermediate transfer belt 50 rotatably driven by a driving roller 52. The toner remaining on the photosensitive drum 41 is collected by the cleaner 45. Note that the image forming process of each color is performed at the timing of superimposing the toner image on the upstream toner image that has been primarily transferred onto the intermediate transfer belt 50.

In parallel with this image forming process, the sheet S is fed from one of the sheet feeding units 10a, 10b, and 10c, and conveyed to the registration unit 3 by one of the extracting units 20a and 20b and the separation roller pair 13 c. The first skew correction section 30 and the second skew correction section 60 are provided in the registration unit 3. The positional deviation and skew of the sheet S are corrected by the registration unit 3, and the sheet S is conveyed to the secondary transfer nip T2 in synchronization with the timing at which the full-color toner image formed on the intermediate transfer belt 50 reaches the secondary transfer nip T2. Then, by applying a secondary transfer bias to the secondary transfer outer roller 54, the full-color toner image on the intermediate transfer belt 50 is transferred onto the first sheet surface (front surface) of the sheet S. That is, the secondary transfer nip T2 is an example of a transfer unit that transfers the toner image carried on the intermediate transfer belt 50 onto the sheet S. It should be noted that the toner remaining on the intermediate transfer belt 50 is collected by the belt cleaner 56. As described above, the image forming unit 40 forms an image on the sheet S that has been conveyed by the registration unit 3.

The sheet S to which the toner image has been transferred is conveyed to the fixing unit 100 by the pre-fixing conveying unit 70. Then, the sheet S is guided to the nip portion of the fixing roller pair 101, and predetermined heat and pressure are applied to melt and bond (fix) the toner. The sheet S having passed through the fixing unit 100 is nipped by the lower cooling belt 111a and the upper cooling belt 111b, which are endless belts, and conveyed by the rotation of the lower driving roller 112a and the upper driving roller 112 b. Then, the sheet S is in contact with the heat sink 113 via the upper cooling belt 111b, and is cooled by transferring heat to the heat sink 113.

Subsequently, the branch conveying unit 120 performs path selection of conveying to the sheet discharge finisher unit 150 or the reverse conveying unit 130. Note that after the sheet S has been conveyed to the reverse conveyance unit 130, the sheet S may also be conveyed to the sheet discharge finisher unit 150 by reversing the sheet S so that the first sheet surface on which an image has been formed in the secondary transfer nip T2 becomes the lower side.

In the case where an image is formed on only one side of the sheet S, the sheet S is conveyed from the branch conveying unit 120 to the sheet discharging finisher unit 150, and curl of the sheet S is corrected by the small-diameter hard roller and the large-diameter soft roller. Subsequently, the sheet S that has passed through the sheet discharge finisher unit 150 is either discharged to the outside of the apparatus or conveyed to a sheet discharge optional apparatus, not shown.

In the case of performing image formation on both surfaces of the sheet S, the sheet S is conveyed to the reverse conveyance unit 130 by the branch conveyance unit 120, and is diverted in the reverse conveyance unit 130. The diverted sheet S is conveyed from the reverse conveying unit 130 to the second duplex conveying unit 140 and the first duplex conveying unit 6, and is guided to the registration unit 3. Thereafter, an image is formed on the second surface (back surface) of the sheet S in the secondary transfer nip T2, and then, the sheet S is discharged either to the outside of the apparatus or to a sheet discharge option apparatus, not shown, via the branch conveying unit 120 and the sheet discharge finisher unit 150.

Control system structure

Next, the configuration of the control system in the printer 1 will be described using fig. 2. Fig. 2 is a block diagram showing a control system of the image forming apparatus of the present embodiment.

The printer 1 includes a control unit 200. Devices such as the computer 300 and various sensors are connected to the control unit 200 so as to be allowed to input signals, and devices such as the imaging unit 40 and various motors are controllably connected.

The control unit 200 includes hardware configurations such as a Central Processing Unit (CPU), a Random Access Memory (RAM), and a Read Only Memory (ROM), but the RAM and the ROM are not shown. In the control unit 200, these hardware configurations are configured such that the storage unit 202, the operation control unit 203, the image forming control unit 204, the sheet conveyance control unit 205, the sensor control unit 206, and the shift control unit 207 perform their respective functions using, for example, programs.

The storage unit 202 may temporarily store various signals and data. The operation control unit 203 is connected to an operation unit such as an operation panel (not shown) provided in the printer 1, and performs control such as inputting a signal from the operation unit and displaying an image. The imaging control unit 204 is connected to the imaging unit 40, and controls the imaging unit 40. The image forming control unit 204 transmits an image signal contained in a print job, for example, transmitted from the computer 300, to the image forming unit 40, and forms a toner image on the intermediate transfer belt 50 as described above while controlling each process cartridge.

The sheet conveyance control unit 205 is connected to, for example, the inclined conveyance roller drive motor 61M1, the pre-registration roller drive motor 31M1, the registration roller drive motor 65M1, the conveyance roller drive motor 32M1, and the separation roller drive motor 10M1, and controls these motors. The inclined conveyance roller driving motor 61M1 is a motor that drives each driving roller of the plurality of inclined conveyance roller pairs 61, 62, and 63, and freely controls the rotational speeds of these roller pairs (i.e., the sheet conveyance speed, including driving and stopping of the inclined conveyance roller pairs 61, 62, and 63). The pre-registration roller driving motor 31M1 is a motor that drives a driving roller of a pre-registration roller pair 31 (pre-registration roller pair) of the registration unit 3. The pre-registration roller drive motor 31M1 freely controls the rotational speed of the pre-registration roller pair (i.e., the sheet conveying speed, including the driving and stopping of the pre-registration roller pair 31). The registration roller driving motor 65M1 is a motor that drives a driving roller of the registration roller pair 65 (registration roller pair) of the registration unit 3, and freely controls the rotational speed of the registration roller pair (i.e., the sheet conveying speed, including driving and stopping of the registration roller pair 65). The conveying roller driving motor 32M1 is a motor that drives each driving roller of the plurality of conveying roller pairs 32 and 33, and freely controls the rotational speed of the conveying roller pairs (i.e., the sheet conveying speed, including driving and stopping of the conveying roller pairs 32 and 33). The separation roller driving motor 10M1 is a motor that drives the separation roller pair 13c of the sheet feeding unit 10 c. The separation roller driving motor 10M1 freely controls the rotation speed of the separation roller pair (i.e., the sheet conveying speed, including driving and stopping of the separation roller pair 13 c). That is, in the printer 1 of the present embodiment, the rotational speeds of the pre-registration roller pair 31, the registration roller pair 65, the plurality of inclined conveyance roller pairs 61, 62, and 63, the plurality of conveyance roller pairs 32 and 33, and the separation roller pair 13c can be freely and independently controlled using motors different from each other.

Further, the sheet conveyance control unit 205 is connected to, for example, the oblique conveyance separation driving motor 61M2, the pre-registration roller separation driving motor 31M2, the registration roller separation driving motor 65M2, and the conveyance roller separation driving motor 32M2, and controls these motors. The inclined conveyance separation driving motor 61M2 performs driving so as to switch the driving rollers and driven rollers of the plurality of inclined conveyance roller pairs 61, 62, and 63 between the nip conveyance state and the non-nip state. Here, the pinch conveying state refers to a state in which the driving rollers and the driven rollers of the plurality of inclined conveying roller pairs 61, 62, and 63 are in pressure contact with each other to pinch and convey the sheet S, and the non-pinch state refers to a state in which the driving rollers and the driven rollers are separated from each other to unclamp the sheet S. The pre-registration roller separation driving motor 31M2 performs driving to switch the driving roller and the driven roller of the pre-registration roller pair 31 between a pinch conveying state in which the driving roller and the driven roller are in pressure contact with each other to pinch and convey the sheet S, and a non-pinch state in which the driving roller and the driven roller are separated from each other to release the pinch of the sheet S. The registration roller separation driving motor 65M2 performs driving to switch the driving roller and the driven roller of the registration roller pair 65 between a pinch conveying state in which the driving roller and the driven roller are in pressure contact with each other to pinch and convey the sheet S, and a non-pinch state in which the driving roller and the driven roller are separated from each other to release the pinch of the sheet S. The conveying roller separation driving motor 32M2 performs driving to switch the driving rollers and driven rollers of the conveying roller pairs 32 and 33 between a pinch conveying state in which the driving rollers and driven rollers are in pressure contact with each other to pinch and convey the sheet S, and a non-pinch state in which the driving rollers and driven rollers are separated from each other to release the pinch of the sheet S. By driving and controlling these motors, the sheet conveyance control unit 205 conveys the sheet to the secondary transfer nip T2 in synchronization with the timing of the toner image on the intermediate transfer belt 50 while performing skew correction of the sheet S.

The sensor control unit 206 is an example of an acquisition unit that acquires information on the length of the sheet S, and inputs signals from sensors (e.g., the conveying sensor 35 and the leading edge detection sensor 66) by being connected to these sensors. Because in the registration unit 3, the conveyance sensor 35 and the leading edge detection sensor 66 input signals, the sensor control unit 206 can acquire information about the position and length of the sheet S.

The shift control unit 207 is connected to the abutment plate shift motor 64SM, the pre-registration roller shift motor 31SM, and the registration roller shift motor 65SM, and performs drive control of these motors. The abutment plate displacement motor 64SM performs drive control of the abutment plate 64 in the width direction perpendicular to the sheet conveying direction. The pre-registration roller shift motor 31SM performs drive control of the pre-registration roller pair 31 in the width direction. The registration roller shift motor 65SM is an example of a moving unit that performs drive control so as to move the registration roller pair 65 in the width direction.

Details of registration unit

The configuration of the registration unit 3 of the present embodiment will be described below. Fig. 3, 4, and 5 are a perspective view, a plan view, and a sectional view, respectively, showing the registration unit 3. Note that in the printer 1 of the present embodiment, as an example, a sheet conveying system with the center as a reference is employed such that a sheet is conveyed by aligning the center of the sheet in the width direction with the center of the sheet conveying path in the direction perpendicular to the sheet conveying direction. The registration unit 3 includes a first skew correction section 30 and a second skew correction section 60. The first skew correction portion 30 is arranged upstream of the second skew correction portion 60 in the sheet conveying direction D1.

The first skew correction section 30 includes a pre-registration roller pair (hereinafter simply referred to as a pre-registration roller pair 31), conveying roller pairs 32 and 33, a Contact Image Sensor (CIS) 34 as a contact image sensor, a conveying sensor 35, and a conveying guide 36. The pre-registration roller pair 31 is an example of a first roller pair, the conveying roller pairs 32 and 33 are examples of a second roller pair that is disposed upstream of the pre-registration roller pair 31 in the sheet conveying direction, and conveys the sheet S. The first skew correction portion 30 may perform the first skew correction operation of the conveyed sheet S by starting rotation of the pre-registration roller pair 31 after the leading edge of the sheet S conveyed by the conveying roller pairs 32 and 33 has abutted against the pre-registration roller pair 31.

Each roller pair sandwiches the sheet S by a driving roller and a driven roller, and conveys the sheet S downstream in the sheet conveying direction D1. That is, the pre-registration roller pair 31 and the conveying roller pairs 32 and 33 are each capable of switching between a nip conveying state in which the sheet S is nipped and conveyed, and a non-nip state in which the nip of the sheet S is released. Each driving roller rotates by receiving driving from the driving motors 31M1 and 32M1 via a transmission gear (not shown), and obtains power for sending the sheet S in the conveying direction. Further, each roller pair can be released by receiving the drive from the separation drive motors 31M2 and 32M2 via a transmission gear (not shown), thereby separating the roller pairs. The pre-registration roller pair 31 is movable in the width direction W perpendicular to the sheet conveying direction D1 by receiving a drive from a pre-registration roller shift motor 31SM via a transmission gear (not shown), and changes position according to the length of the sheet S in the width direction W.

The second skew correction section 60 includes inclined conveyance roller pairs 61, 62, and 63, an abutment plate 64, a registration roller pair 65, a leading edge detection sensor 66, and a conveyance guide 67. The abutment plate 64 is an example of a contact surface that extends in the sheet conveying direction and is capable of contacting an end portion in the width direction of the sheet S. The registration roller pair 65 is an example of a third roller pair disposed downstream of the inclined conveyance roller pairs 61, 62, and 63 in the sheet conveyance direction. The inclined conveying roller pairs 61, 62, and 63 are examples of a steering roller pair that moves the sheet S in a direction inclined with respect to the sheet conveying direction so as to approach the abutment plate 64 in the width direction toward the downstream in the sheet conveying direction. The second skew correction portion 60 can perform a second skew correction operation by moving the sheet S along the abutment plate 64 so as to correct skew of the sheet S and convey the sheet.

Each roller pair sandwiches the sheet S by a driving roller and a driven roller, and conveys the sheet S downstream in the sheet conveying direction D1. That is, the pair of inclined conveying rollers 61, 62, and 63 and the pair of registration rollers 65 can be switched between a nip conveying state in which the sheet S is nipped and conveyed, and a non-nip state in which the nip of the sheet S is released. Each driving roller rotates by receiving driving from the driving motors 61M1 and 65M1 via a transmission gear (not shown), and obtains power to send the sheet S in the conveying direction. Further, each roller pair can be released by receiving the drive from the separation drive motors 61M2 and 65M2 via a transmission gear (not shown), thereby separating the roller pairs. The registration roller pair 65 can be moved in the width direction perpendicular to the sheet conveying direction D1 by receiving a drive from the registration roller shift motor 65SM via a transmission gear (not shown), and change position according to the length of the sheet S in the width direction. The abutment plate 64 can be moved in the width direction by receiving a drive from the abutment plate displacement motor 64SM via a transmission gear (not shown), and the position is changed according to the length of the sheet S in the width direction.

A secondary transfer nip T2 (see fig. 1) formed by the secondary transfer outer roller 54 and the intermediate transfer belt 50 is arranged downstream of the registration roller pair 65 in the sheet conveying direction D1, and transfers an image onto the sheet S. That is, the second skew correction portion 60 is arranged upstream of the image forming unit 40 in the sheet conveying direction, and the registration unit 3 conveys the sheet S to the secondary transfer nip T2. Note that, in the present embodiment, the conveying roller 37 and the conveying guide 38 are disposed between the first skew correction portion 30 and the second skew correction portion 60 in the sheet conveying direction. However, by closely arranging the first skew correction portion 30 and the second skew correction portion 60 in the sheet conveying direction, the conveying roller 37 and the conveying guide 38 can be removed.

Registration correction (non-long sheet)

Registration correction of the no-long sheet will be described below. Here, the non-long sheet refers to a standard-sized sheet, for example, an A4-sized sheet having a length of about 30 inches or less in the sheet conveying direction. However, needless to say, the non-long sheet is not limited to a standard-sized sheet. Based on the information on the length of the sheet S acquired by the sensor control unit 206, the control unit 200 controls the first skew correction portion 30 and the second skew correction portion 60.

Fig. 6A to 7B are plan views illustrating the registration unit 3, and illustrate skew correction operations of the non-long sheets of the sheet S in time series. Further, the traveling direction of the chronological sheet S is shown by arrow directions d1, d2, d3, and d 4. Here, with regard to the plan view of the rollers in fig. 6A to 7B, a black (solid) roller indicates a roller in a nip conveyance state in which a sheet is nipped and conveyed, and a white roller indicates a roller in a non-nip state in which the nip of the sheet S is released. As shown in fig. 6A, the control unit 200 conveys the sheet S by bringing the pre-registration roller pair 31 into a nip conveyance state. When the sheet S has reached the inclined conveying roller pairs 61, 62, and 63 in a skewed state, the sheet S is brought into contact with the abutment plate 64 by a force applied by the inclined conveying roller pairs 61, 62, and 63 in a width direction perpendicular to the conveying direction.

As shown in fig. 6B, since the sheet S receives the reaction force of the contact force from the abutment plate 64 when the sheet contacts the abutment plate 64 by the inclined conveyance roller pairs 61, 62, and 63, and slides and rotates to follow the abutment plate 64, skew is corrected. Note that the position of the abutment plate 64 is adjusted based on information of the end position of the sheet S read by the CIS 34 provided upstream of the inclined conveyance roller pairs 61, 62, and 63 in the sheet conveyance direction. After the leading edge of the sheet has reached the inclined conveyance roller pairs 61, 62, and 63, the control unit 200 brings the registration front roller pair 31 into a non-nip state. Further, after the leading edge of the sheet conveyed by the pre-registration roller pair 31 has reached the inclined conveying roller pairs 61, 62, and 63, the control unit 200 brings the conveying roller pairs 32 and 33 into a non-nip state. That is, at the time of correcting skew by the inclined conveying roller pairs 61, 62, and 63, the pre-registration roller pair 31 and the conveying roller pairs 32 and 33 disposed upstream of the inclined conveying roller pairs in the sheet conveying direction have been separated, thereby releasing the nip in advance. Since by separating the rollers, the sheet S is not subjected to resistance from the roller nip when the sheet is moved and rotated in the width direction by the inclined conveyance roller pair, wrinkles and folds in the sheet S can be avoided.

As shown in fig. 7A, when the leading edge of the sheet S reaches the registration roller pair 65, the registration roller pair 65 is laterally moved in the width direction W shown by the arrow W1 direction in fig. 7A to align the position in the width direction of the sheet S with the position in the width direction of the image conveyed to the secondary nip T2. Further, by comparing the detection result of the leading edge of the sheet S in the conveying direction detected by the leading edge detection sensor 66 with the timing of the image conveyed to the secondary nip T2, the speed or timing of the registration roller pair 65, or both the speed and timing, is controlled so that the positions of the image and the leading edge of the sheet S are aligned. At the time of the lateral registration shift of the sheet S, in order not to apply unnecessary force, the pair of inclined conveying rollers 61, 62, and 63 are also separated, thereby releasing the nip.

As shown in fig. 7B, when the sheet S has been conveyed to the secondary transfer nip T2, the registration roller pairs are also separated, and all upstream roller pairs in the sheet conveying direction enter a state of releasing the nip. Since the secondary transfer nip T2 does not receive a force from any upstream roller pair via the sheet S by separating all upstream roller pairs, the sheet S can be conveyed accurately while transferring an image onto the sheet S. That is, in the case of an unfinished sheet having a length in the conveying direction of the conveyed sheet equal to or smaller than a predetermined length (for example, equal to or smaller than 30 inches), the control unit 200 performs a second skew correction operation in which skew is corrected by moving the sheet S along the abutting plate 64 using the second skew feeding correction portion 60. In the second skew correction operation performed by the second skew correction portion 60, the control unit 200 controls such that the registration roller pair 65 nips the sheet S that has moved along the abutment plate 64. Then, using the registration roller shift motor 65SM, as indicated by an arrow d4 in fig. 7B, the position in the width direction of the sheet nipped by the registration roller pair 65 is corrected. Further, in the case of conveying an unread sheet, in the second skew correction operation of the second skew correction portion 60, the control unit 200 changes the sheet conveying speed of the registration roller pair 65 corresponding to the timing of image formation by the image forming unit 40. The timing here refers to, for example, the timing at which the toner image reaches the secondary transfer nip T2.

Registration correction (Long sheet)

Next, registration correction of the long sheet will be described. Fig. 8A, 9A, and 10A are plan views showing the registration unit 3, and fig. 8B, 9B, and 10B are sectional views showing the registration unit 3. Fig. 8A to 10B illustrate the skew correction operation of the sheet S in the case of a long sheet in time series. Here, with regard to the plan view of the rollers in fig. 8A, 9A, and 10A, a black (solid) roller indicates a roller in a nip conveyance state in which a sheet is nipped and conveyed, and a white roller indicates a roller in a non-nip state in which the nip of the sheet S is released. As shown in fig. 8A and 8B, when the leading edge of the sheet S has reached the pre-registration roller pair 31, the driving of the pre-registration roller pair 31 is stopped and the leading edge of the sheet S abuts against the nip portion of the pre-registration roller pair 31 for the duration of a predetermined time measured using the detection position of the conveyance sensor 35 as a reference. At this time, since the conveying roller pairs 32 and 33, which are more upstream than the pre-registration roller pair 31 in the sheet conveying direction, are driving, the sheet S forms a bend (loop) L1, as shown in fig. 9A and 9B. By receiving the reaction force of the loop L1 that has been formed, the leading edge of the sheet S pivots about the pre-registration roller pair 31 as a start point, and the leading edge of the sheet S follows the axial direction (i.e., the width direction W) of the pre-registration roller pair 31, thereby correcting skew of the sheet.

Here, in the conveying guide 36 located upstream of the pre-registration roller pair 31 in the sheet conveying direction, a curved space portion 36a is provided, the curved space portion 36a being an annular space for partially expanding the cross section of the conveying unit. Thus, since the loop L1 as a bend (curve) is formed in the sheet S, wrinkles and folds are prevented from occurring in the sheet S. That is, the first skew correction portion 30 includes a curved space portion 36a for forming a loop L1 of the sheet S generated when the sheet S abuts against the registration front roller pair 31. Note that, in the present embodiment, the sheet conveying path of the first skew correction portion 30 is in a substantially horizontal shape, and the curved space portion 36a is provided above the sheet conveying path. However, it is acceptable that the curved space portion 36a is provided below the sheet conveying path.

The pre-registration roller pair 31 is arranged at a position more upstream than the inclined conveying roller pairs 61, and 63 in the sheet conveying direction, and performs registration correction. That is, in the case of conveying a long sheet having a length in the sheet conveying direction longer than a predetermined length (for example, 30 inches), the control unit 200 performs the first skew correction operation using the first skew correction portion 30. As shown in fig. 10A and 10B, in the case of conveying a long sheet, the control unit 200 brings the inclined conveying roller pairs 61, and 63 into a non-nip state. Thereby, the sheet whose skew has been corrected is conveyed straight to the secondary transfer nip T2.

As described above, in the present embodiment, in the case of conveying a long sheet, skew of the sheet is corrected by abutting the leading edge of the sheet against the registration front roller pair 31 using the first skew correction portion 30. On the other hand, in the case of conveying an unread sheet, by abutting the side edge of the sheet against the abutment plate while conveying the sheet, the skew of the sheet is corrected using the second skew correction portion 60.

Regarding long sheets exceeding 30 inches, the reason why the second skew correction portion 60 cannot convey the sheets obliquely will be described using fig. 12. Fig. 12 is a diagram showing a state in which the inclined conveyance of the long sheet starts. When the sheet starts to be obliquely conveyed when the leading edge of the sheet reaches the oblique-conveying-roller pairs 61, 62, and 63, the trailing edge of the sheet is in a state nipped by the separation-roller pair 13 c. If the sheet starts to be obliquely conveyed by the oblique-conveying-roller pairs 61, 62, and 63 in this state while the leading-edge side of the sheet S tries to be obliquely conveyed, the trailing-edge side of the sheet S is in a state nipped by the separation-roller pair 13c, so that wrinkles and folds occur in the sheet S. Without a long sheet, the trailing edge of the sheet S is not nipped by the separation roller pair 13 c. That is, the trailing edge of the sheet S is located at a position not nipped by the separation roller pair 13c but nipped by the conveying roller pairs 32 and 33. In this case, since the conveying roller pairs 32 and 33 can be switched between the nip state and the non-nip state, skew of the sheet S can be corrected by the second skew correction portion 60.

Further, when feeding a plurality of sheets S, the separation roller pair 13c cannot transit from the nip state to the non-nip state. The reason for this is because the separation roller pair 13c has a function of separating the plurality of sheets S loaded on the loading tray 11c one by one. If the separation roller pair 13c enters the non-nip state, it is possible to convey the preceding sheet while also conveying the following sheet. The latter sheet is conveyed together with the former sheet is a so-called double feed phenomenon, and means defective conveyance. Therefore, in the case of conveying a plurality of sheets S, it is impossible to bring the separation roller pair 13c into the non-nip state. Although skew correction of a long sheet can be performed by the second skew correction portion 60 if the section of the conveying roller pair 32 and 33 is enlarged in the sheet conveying direction, this obviously results in an increase in the apparatus size.

Further, in the present embodiment, the sheet S having a length exceeding 30 inches is referred to as a long sheet. Thereby, the distance Y from the separation roller pair 13c to the inclined conveyance roller pair 61 can be set to 30 inches. That is, in the case where the sheet length exceeds 30 inches, the trailing edge of the sheet S is nipped by the separation roller pair 13c at the start of the inclined conveyance. On the other hand, in the case where the sheet length is shorter than 30 inches, the trailing edge of the sheet S is not nipped by the separation roller pair 13c at the start of the inclined conveyance.

Although in the present embodiment, the second skew correction section 60 uses the oblique-conveyance registration unit as the skew correction unit, it is not limited thereto. Regarding the second skew correction section 60, not only a method using an oblique transfer registration unit, but also a registration method based on a speed difference or a registration method based on a wobble shift, for example, may be applied. That is, any active registration method of correcting skew of a sheet while conveying the sheet (active) may be applied to the second skew correction portion.

For example, a registration method based on a velocity difference will be described using fig. 13. Fig. 13 is a plan view illustrating a case of the registration unit in which a registration method based on a velocity difference is applied as the second skew correction section 160. The second skew correction portion 160 includes a first conveying roller pair 161, a second conveying roller pair 162a, and third and fourth conveying roller pairs 162b, 163 in order from the upstream side in the sheet conveying direction. The second conveying roller pair 162a and the third conveying roller pair 162b are arranged on the same axis, but are driven by different motors, so that these roller pairs can be driven independently of each other. When the sheet S has been conveyed to the second skew correction portion 160, the sheet S is further conveyed by the first conveying roller pair 161, and reaches the second conveying roller pair 162a and the third conveying roller pair 162b. At this time, the degree of skew of the sheet S is determined based on the detection result of a sensor (not shown), and accordingly, the rotational speed of each of the second conveying roller pair 162a and the third conveying roller pair 162b is changed. For example, control such as keeping the rotation speed of the second conveying roller pair 162a constant and reducing the rotation speed of the third conveying roller pair 162b is performed. Thus, after correcting the skew of the sheet S, the sheet S is conveyed to the fourth conveying roller pair 163. According to this second skew correction portion 160, skew can be corrected without stopping the sheet S.

Next, a registration method based on the wobble shift will be described using fig. 14. Fig. 14 is a plan view illustrating a case of the registration unit, in which a registration method based on a wobble shift is applied as the second skew correction portion 260. The second skew correction portion 260 includes a conveying roller pair 261 and a swing shift roller pair 262 in order from the upstream side in the sheet conveying direction. The swing shift roller pair 262 is pivotable (swingable) about an axis in a direction perpendicular to the sheet surface as a center, and is movable (displaceable) in the width direction, and is controlled by the control unit 200. When the sheet S has been conveyed to the second skew correction portion 260, the sheet S is further conveyed by the conveying roller pair 261 and reaches the swing shift roller pair 262. At this time, the degree of skew of the sheet S is determined based on the detection result of a sensor (not shown), and accordingly, the swing shift roller pair 262 swings and shifts. Thereby, after correcting the skew of the sheet S, the sheet S is conveyed to a downstream roller pair in the sheet conveying direction. According to this second skew correction portion 260, skew can be corrected without stopping the sheet S.

In the present embodiment, in the case of conveying a long sheet, in the first skew correction operation performed by the first skew correction section 30, the control unit 200 starts rotation of the pre-registration roller pair 31 at a timing corresponding to the timing of image formation performed by the image forming unit 40. The timing here is, for example, the timing at which the toner image reaches the secondary transfer nip T2.

Here, since it is necessary to temporarily stop the sheet S when performing registration correction by abutting the sheet against the pre-registration roller pair 31, it is possible to enlarge the distance between sheets and reduce productivity when the continuous sheet passes. To avoid this, after registration correction of the sheets S has been completed, it is desirable to shorten the distance between the sheets by accelerating the conveyance speed of the sheets S to a speed faster than the transfer conveyance speed. That is, for example, in the case of conveying a sheet that is not long, the control unit 200 conveys the sheet at the first speed in the second skew correction portion 60. On the other hand, in the case of conveying a long sheet, the control unit 200 causes the sheet to pass through the second skew correction portion 60 at a second speed faster than the first speed. Therefore, even in the case of conveying long sheets, it is possible to shorten the distance between sheets and reduce the reduction in productivity as compared with the case of conveying at the first speed. As an example of the second speed, for example, a speed about several tens percent faster than the sheet conveying speed in the secondary transfer nip T2 may be applied.

As shown in fig. 10B, the distance from the pre-registration roller pair 31 to the sheet conveying path of the secondary transfer nip T2 is referred to as a distance X. As shown in fig. 10A and 10B, since in the present embodiment, the pre-registration roller pair 31 is arranged upstream of the inclined conveying roller pairs 61, 62, and 63 in the sheet conveying direction, a sufficient length of the distance X can be ensured to accelerate the sheet S that has been temporarily stopped. On the other hand, in the case where the pre-registration roller pair 31 is arranged downstream of the inclined conveyance roller pairs 61, 62, and 63, a sufficient length of the distance X cannot be ensured to accelerate the sheet S that has been temporarily stopped. Therefore, it is easier to shorten the distance between sheets as compared with the case where the pre-registration roller pair 31 is arranged downstream of the inclined conveyance roller pairs 61, 62, and 63, and by reducing the reduction in productivity, the productivity can be improved.

Registration correction processing step

The processing steps of registration correction in the present disclosure will be described using the flowchart shown in fig. 11. First, upon receiving a print execution instruction from a user via, for example, the computer 300, the control unit 200 starts a print job (step S1). In addition to the instruction of the number of prints, the user can specify the type of sheet or the like for printing.

The control unit 200 starts feeding the sheet S (step S2), and recognizes whether the sheet type in the print job is a long sheet (step S3). In the case where the control unit 200 judges that the sheet S is not a long sheet but is not a long sheet (step S3: no), the control unit 200 brings the conveying roller pairs 32 and 33 and the pre-registration roller pair 31 into a non-nip state by separating the conveying roller pairs 32 and 33 and the pre-registration roller pair 31 (step S4), and corrects skew and lateral registration by tilting the conveying roller pairs 61, 62, and 63 (step S5). Thereafter, the final lateral registration position of the sheet S is moved to be aligned with the image position by the registration roller pair 65 (step S6).

On the other hand, in the case where the control unit 200 determines that the sheet S is a long sheet (yes in step S3), the conveyance sensor 35 detects the leading edge of the sheet S (step S7). Based on the detection timing of the conveyance sensor 35, the control unit 200 corrects skew by abutting the leading edge of the sheet S against the registration front roller pair 31 (step S8). Then, the control unit 200 resumes conveyance of the sheet S, which has been temporarily stopped, to the downstream side in the sheet conveyance direction so as to coincide with the timing at which the toner image reaches the secondary transfer nip T2 (step S9).

Thereafter, the control unit 200 transfers the image in the secondary transfer nip T2 without the long sheet and the sheet S of the long sheet (step S10). Further, the control unit 200 performs fixing (step S11), and discharges or inverts the sheet according to the print job (step S12), and determines whether or not there is a subsequent sheet (step S13). In the case where the control unit 200 determines that there is a subsequent sheet (yes at step S13), the control unit 200 again recognizes whether the sheet type in the print job is a long sheet (step S3). In the case where the control unit 200 determines that there is no subsequent sheet (no in step S13), the control unit 200 ends the print job (step S14).

Note that, in the present embodiment, for example, in the case of conveying an indefinite sheet, the skew correction processing by the first skew correction section 30 is not performed, but is not limited thereto, and even if the sheet is an indefinite sheet, the skew correction processing by the first skew correction section 30 may be performed. Thus, for example, even in the case of conveying a sheet such as a special sheet (e.g., such as thin paper and cardboard) in which the accuracy of the skew correction by the second skew correction portion 60 may be lowered, the skew correction can be performed with high accuracy by the first skew correction portion 30. That is, as described in the present embodiment, the skew of the non-long sheet is corrected in the second skew correction portion 60, while the skew of the long sheet is corrected in the first skew correction portion 30, which is only one example.

As described above, according to the printer 1 of the present embodiment, the first skew correction portion 30 is arranged upstream of the second skew correction portion 60 in the sheet conveying direction D1. Therefore, since the inclined conveying roller pairs 61, 62, and 63 do not perform skew correction when conveying a long sheet, occurrence of wrinkles, folds, and skew can be suppressed. Further, it is not necessary to provide a separate driving configuration to all of the plurality of conveying roller pairs, and an increase in cost, an increase in equipment size, and an increase in process complexity due to an increase in the number of components can be avoided. As described above, by performing registration correction of a long sheet by the pre-registration roller pair 31, the posture of the sheet can be corrected with high accuracy. Therefore, the skew of the sheet can be corrected with high accuracy while suppressing an increase in the size and cost of the apparatus.

Further, according to the printer 1 of the present embodiment, the pre-registration roller pair 31 is arranged upstream of the second skew correction portion 60 in the sheet conveying direction. Therefore, the distance between the pre-registration roller pair 31 and the secondary transfer nip T2 can be prolonged as compared with the case where the sheet abuts against the roller pair arranged downstream of the inclined conveyance roller pair. Therefore, since a long acceleration section from the pre-registration roller pair 31 to the secondary transfer nip T2 can be provided, a sheet gap generated corresponding to the stop time of the sheet that has been temporarily stopped at the pre-registration roller pair 31 can be shortened. Therefore, the decrease in productivity can be reduced.

In the above-described embodiment, the positions of the CIS 34, the transfer sensor 35, and the leading edge detection sensor 66 are not limited to those described in the present embodiment. That is, these sensors may be arranged at any position upstream of the secondary transfer nip T2 in the conveying direction so that skew of the sheet is corrected before the sheet reaches the secondary transfer nip T2.

According to the present embodiment, the skew of the sheet can be corrected with high accuracy while suppressing an increase in the size and cost of the apparatus.

Other embodiments

While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims (14)

1. A sheet conveying apparatus comprising:

a first skew correction portion including a first roller pair configured to convey a sheet and a second roller pair disposed upstream of the first roller pair in a sheet conveying direction and configured to convey the sheet, the first skew correction portion being configured to correct skew of the sheet conveyed by the second roller pair by abutting a leading edge of the sheet against the first roller pair to form a bend in the sheet;

A second skew correction portion including a pair of steering rollers configured to convey the sheet, the second skew correction portion configured to correct skew of the sheet by conveying the sheet in a steering motion using the pair of steering rollers;

an acquisition unit configured to acquire information about a sheet length; and

a control unit configured to control the first skew correction portion and the second skew correction portion based on the information on the sheet length acquired by the acquisition unit,

wherein, in the case of conveying a first sheet of a first length, the control unit is configured to correct skew of the first sheet by the second skew correction portion, and

wherein, in the case of conveying a second sheet of a second length longer than the first length, the control unit is configured to correct skew of the second sheet by the first skew correction portion, and is configured not to correct skew of the second sheet by the second skew correction portion.

2. The sheet conveying apparatus according to claim 1, wherein the second skew correction portion is provided downstream of the first skew correction portion in a sheet conveying direction.

3. The sheet conveying apparatus according to claim 1 or 2,

Wherein, in the case of conveying a second sheet having a length longer than a predetermined length in the sheet conveying direction, the control unit is configured to correct skew of the second sheet by the first skew correction portion, and

wherein, in the case of conveying the first sheet having a length in the sheet conveying direction equal to or smaller than the predetermined length, the control unit is configured to correct skew of the first sheet by the second skew correction portion.

4. The sheet conveying apparatus according to claim 3, wherein the predetermined length is 30 inches.

5. The sheet conveying apparatus according to claim 1 or 2,

wherein the second skew correction portion includes a contact surface extending in a sheet conveying direction,

wherein the contact surface is configured to contact an end portion of the sheet to be conveyed in a width direction perpendicular to the sheet conveying direction,

wherein the steering roller pair includes an inclined conveying roller pair configured to move a sheet in a direction inclined with respect to the sheet conveying direction, the direction being inclined to approach the contact surface in the width direction toward a downstream side of the sheet conveying direction, and

wherein the second skew correction portion is configured to convey the sheet by moving the sheet along the contact surface using the pair of inclined conveyance rollers to correct skew of the sheet.

6. The sheet conveying apparatus according to claim 3,

wherein the second skew correction portion includes a contact surface extending in a sheet conveying direction,

wherein the contact surface is configured to contact an end portion of the sheet to be conveyed in a width direction perpendicular to the sheet conveying direction,

wherein the steering roller pair includes an inclined conveying roller pair configured to move the sheet in a direction inclined with respect to the sheet conveying direction so as to approach the contact surface in the width direction toward a downstream side in the sheet conveying direction,

wherein the second skew correction portion is configured to convey the sheet by moving the sheet along the contact surface using the pair of inclined conveying rollers to correct skew of the sheet,

wherein the inclined conveying roller pair is configured to change between a nip conveying state in which the sheet is nipped and conveyed, and a non-nip state in which the nip of the sheet is released, and

wherein, in a case where the length of the sheet in the sheet conveying direction is longer than a predetermined length, the control unit is configured to change the inclined conveying roller pair to the non-nip state.

7. The sheet conveying apparatus according to claim 3,

wherein the second skew correction portion is disposed upstream of the image forming unit in the sheet conveying direction, and

wherein, in a case where the length of the sheet in the sheet conveying direction is longer than a predetermined length, in the skew correction operation of the first skew correction portion, the control unit is configured to start rotation of the first roller pair at a timing corresponding to the image forming timing of the image forming unit.

8. The sheet conveying apparatus according to claim 3,

wherein the second skew correction portion includes a contact surface extending in a sheet conveying direction,

wherein the contact surface is configured to contact an end portion of the sheet to be conveyed in a width direction perpendicular to the sheet conveying direction,

wherein the steering roller pair includes an inclined conveying roller pair configured to move the sheet in a direction inclined with respect to the sheet conveying direction so as to approach the contact surface in the width direction toward a downstream side in the sheet conveying direction,

wherein the second skew correction portion is configured to convey the sheet by moving the sheet along the contact surface using the pair of inclined conveying rollers so as to correct skew of the sheet,

Wherein the first roller pair is configured to change between a nip conveying state in which the sheet is nipped and conveyed, and a non-nip state in which the nip of the sheet is released, and

wherein, in a case where the length of the sheet in the sheet conveying direction is equal to or smaller than a predetermined length, the control unit is configured to convey the sheet by changing the first roller pair to the nip conveying state, and after the leading edge of the sheet has reached the inclined conveying roller pair, the control unit is configured to change the first roller pair to the non-nip state.

9. The sheet conveying apparatus according to claim 8,

wherein the second roller pair is configured to change between a nip conveying state in which the sheet is nipped and conveyed and a non-nip state in which the nip of the sheet is released, and

wherein, in a case where the length of the sheet in the sheet conveying direction is equal to or smaller than the predetermined length, after the leading edge of the sheet conveyed by the first roller pair has reached the inclined conveying roller pair, the control unit is configured to change the second roller pair to the non-nip state.

10. The sheet conveying apparatus according to claim 5,

Wherein the second skew correction portion includes a third roller pair disposed downstream of the inclined conveying roller pair in the sheet conveying direction and a moving unit configured to move the third roller pair in the width direction, and

wherein in the skew correction operation by the second skew correction portion, the control unit is configured to control so that the third roller pair nips the sheet that has been moved along the contact surface, and control so that the moving unit corrects a position in a width direction of the sheet nipped by the third roller pair.

11. The sheet conveying apparatus according to claim 3,

wherein the second skew correction portion includes a contact surface extending in a sheet conveying direction,

wherein the contact surface is configured to contact an end portion of the sheet to be conveyed in a width direction perpendicular to the sheet conveying direction,

wherein the steering roller pair includes an inclined conveying roller pair configured to move the sheet in a direction inclined with respect to the sheet conveying direction so as to approach the contact surface in the width direction toward a downstream side in the sheet conveying direction,

Wherein the second skew correction portion is configured to convey the sheet by moving the sheet along the contact surface using the pair of inclined conveying rollers to correct skew of the sheet,

wherein the second skew correction portion includes a third roller pair disposed downstream of the inclined conveying roller pair in a sheet conveying direction and a moving unit configured to move the third roller pair in a width direction,

wherein in the skew correction operation by the second skew correction portion, the control unit is configured to control so that the third roller pair nips the sheet moving along the contact surface, and control so that the moving unit corrects a position in a width direction of the sheet nipped by the third roller pair,

wherein the second skew correction portion is disposed upstream of the image forming unit in the sheet conveying direction, and

wherein, in a case where the length of the sheet in the sheet conveying direction is equal to or smaller than the predetermined length, in the skew correction operation of the second skew correction portion, the control unit is configured to control such that the sheet conveying speed of the third roller pair is changed at a timing corresponding to the image forming timing of the image forming unit.

12. The sheet conveying apparatus according to claim 1 or 2, wherein the first skew correction portion includes a curved space portion at which the sheet is curved by the sheet abutting against the first roller pair.

13. An image forming apparatus comprising:

the sheet conveying apparatus according to claim 1 or 2; and

an image forming unit configured to form an image on a sheet that has been conveyed by the sheet conveying apparatus.

14. An imaging apparatus according to claim 13,

wherein the image forming unit includes an image bearing member configured to bear a toner image and a transfer unit configured to transfer the toner image borne by the image bearing member onto a sheet, an

Wherein the sheet conveying apparatus is configured to convey a sheet to a transfer unit.