SHEET CONVEYANCE APPARATUS

Abstract

A sheet conveyance apparatus includes a conveyance roller, an abutment member including an abutment surface, an obliquely conveying roller configured to convey the sheet such that the side edge portion is moved toward the abutment surface, a sheet side-edge detection portion, and a controller. The controller is configured to control the conveyance force of the obliquely conveying roller at a first conveyance force until a predetermined time has elapsed, in an abutment operation in which the sheet is abutted against the abutment surface by the obliquely conveying roller, and control the conveyance force of the obliquely conveying roller at a second conveyance force larger than the first conveyance force if the predetermined time has elapsed and the position of the side edge portion of the sheet detected by the sheet side-edge detection portion is out of a predetermined range.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a sheet conveyance apparatus that conveys sheets.

Description of the Related Art

Japanese Patent Application Publication No. H11-189355 proposes an image forming apparatus that includes a feeding portion that feeds a sheet, a sheet alignment portion that corrects the posture of a sheet that is being conveyed, and a registration portion that sends a sheet whose posture has been corrected in the sheet alignment portion, at a predetermined timing. The image forming apparatus also includes an image transfer portion that transfers an image onto a sheet sent by the registration portion, and a fixing portion that fixes the image having been transferred onto the sheet by the image transfer portion, to the sheet.

The sheet alignment portion includes obliquely conveying rollers, conveyance rollers, a sheet-passage detection sensor, and a sheet side-edge detection sensor. The obliquely conveying rollers convey a sheet toward a reference guide; the conveyance rollers move a sheet in a width direction orthogonal to a sheet conveyance direction; and the sheet side-edge detection sensor detects the position of a side edge of a sheet. The obliquely conveying rollers convey a sheet such that the sheet is aligned with the reference guide, and thereby corrects the skew of the sheet. The conveyance rollers move a sheet in the width direction, depending on a detection signal from the sheet side-edge detection sensor, to a position at which the side edge of the sheet is not detected by the sheet side-edge detection sensor.

The sheet alignment portion described in Japanese Patent Application Publication No. H11-189355 is a sheet conveyance apparatus that causes the obliquely conveying rollers to convey a sheet such that the sheet is aligned with the reference guide. In such a sheet conveyance apparatus, after the sheet abuts against the reference guide, the sheet is conveyed while the obliquely conveying rollers slip on the sheet. Thus, such a sheet conveyance apparatus is easily affected by the conveyance resistance of the sheet when the sheet is conveyed by the obliquely conveying rollers. If the sheet has a large conveyance resistance, the conveyance of the sheet performed by the obliquely conveying rollers may be delayed. If the conveyance of the sheet is delayed, the sheet will not reach a roller (located downstream of the obliquely conveying rollers) in a predetermined time, decreasing the productivity.

SUMMARY OF THE INVENTION

According to one aspect to the present invention, a sheet conveyance apparatus includes a conveyance roller configured to convey a sheet, an abutment member including an abutment surface and configured to correct skew of the sheet, the abutment surface being disposed downstream of the conveyance roller and extending along a sheet conveyance direction, the abutment surface being a surface against which a side edge portion of the sheet in a width direction orthogonal to the sheet conveyance direction abuts, an obliquely conveying roller disposed downstream of the conveyance roller in the sheet conveyance direction and configured to convey the sheet such that the side edge portion is moved toward the abutment surface, a sheet side-edge detection portion configured to detect a position of the side edge portion of the sheet in the width direction and change an output value in accordance with the position of the side edge portion of the sheet conveyed by the obliquely conveying roller, and a controller configured to control conveyance force applied by the obliquely conveying roller in the width direction of the sheet, in accordance with a detection result from the sheet side-edge detection portion. The controller is configured to control the conveyance force of the obliquely conveying roller at a first conveyance force until a predetermined time has elapsed, in an abutment operation in which the sheet is abutted against the abutment surface by the obliquely conveying roller, and control the conveyance force of the obliquely conveying roller at a second conveyance force larger than the first conveyance force if the predetermined time has elapsed and the position of the side edge portion of the sheet detected by the sheet side-edge detection portion is out of a predetermined range.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a printer of a first embodiment.

FIG. 2 is a schematic diagram illustrating a registration unit of the first embodiment.

FIG. 3 is a block diagram illustrating control blocks of the first embodiment.

FIG. 4 is a flowchart illustrating an abutment operation performed by the registration unit of the first embodiment.

FIG. 5 is a diagram illustrating conveyance of a sheet performed by a conveyance roller portion of the first embodiment.

FIG. 6 is a diagram illustrating conveyance of a sheet performed by an obliquely-conveying roller portion of the first embodiment.

FIG. 7 is a diagram illustrating a case in which normal control is performed in the registration unit of the first embodiment.

FIG. 8 is a diagram illustrating a state in which the abutment operation has been completed in the registration unit of the first embodiment.

FIG. 9 is a diagram illustrating a case in which recovery control is performed in the registration unit of the first embodiment.

FIG. 10 is a diagram illustrating conveyance of a sheet performed by a registration roller pair in the registration unit of the first embodiment.

FIG. 11 is a graph illustrating the output value from a CIS that changes with time, and that is obtained in a case where the normal control is performed in the registration unit of the first embodiment.

FIG. 12 is a graph illustrating the output value from the CIS that changes with time, and that is obtained in a case where the recovery control is performed in the registration unit of the first embodiment.

FIG. 13 is a flowchart illustrating an abutment operation performed by a registration unit of a second embodiment.

FIG. 14 is a flowchart illustrating an abutment operation performed by a registration unit of a third embodiment.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

Overall Configuration

First, an embodiment of the present invention will be described. Full-color image forming apparatuses are classified into a tandem system and a rotary system. In the tandem system, a plurality of process cartridges is arranged side by side; in the rotary system, a plurality of process cartridges is arranged cylindrically. In addition, the image forming apparatuses are classified, regarding the transfer system, into a direct transfer system and an intermediate transfer system. In the direct transfer system, a toner image is directly transferred from a photosensitive member onto a sheet; in the intermediate transfer system, a toner image is temporarily transferred onto an intermediate transfer belt and then transferred from the intermediate transfer belt onto a sheet. Image forming apparatuses classified as the intermediate transfer system eliminate the need of holding a sheet on a transfer drum, and thus can form images on a variety of types of sheets, such as thick paper sheets and coated sheets. In addition, the image forming apparatuses classified as the intermediate transfer system enable the plurality of process cartridges to perform parallel processing, and transfer a full-color image at a time. Thus, the image forming apparatuses classified as the intermediate transfer system are suitable for achieving high productivity.

As illustrated in FIG. 1, a printer 1 that serves as an image forming apparatus of a first embodiment is an electrophotographic full-color laser-beam printer classified as the tandem-type intermediate-transfer system. The printer 1 includes a feeding unit 13, a conveyance unit 141, a registration unit 144, an image forming unit 11, a fixing unit 12, and a branch-and-conveyance unit 146. The printer 1 further includes a reverse conveyance unit 147, a duplex conveyance unit 149, a discharging tray 148, and an escape tray 152.

The image forming unit 11 includes four process cartridges 10Y, 10M, 10C, and 10Bk. The four process cartridges are used for forming four toner images of yellow (Y), magenta (M), cyan (C), and black (Bk). In addition, the image forming unit 11 includes exposure apparatuses 104a, 104b, 104c, and 104d. Note that the four process cartridges 10Y, 10M, 10C, and 10Bk are the same as each other, except that they produce different colors of image. For this reason, the configuration and the image forming process of only the process cartridge 10Y will be described, and the description for the process cartridges 10M, 10C, and 10Bk will be omitted.

The process cartridge 10Y includes a photosensitive drum 101a, a charging roller, a development unit 102a, and a cleaner 103a. The photosensitive drum 101a has an organic photoconductive layer formed on the outer surface of an aluminum cylinder, and is rotated by a driving motor toward a direction indicated by an arrow A. The image forming unit 11 also includes an intermediate transfer belt 111 that is rotated by a driving roller 115 toward a direction indicated by an arrow B. The intermediate transfer belt 111 is wound around a tension roller 116, the driving roller 115, and a secondary transfer inner roller 113. Inside the intermediate transfer belt 111, primary transfer rollers 112a, 112b, 112c, and 112d are disposed; outside the intermediate transfer belt 111, a secondary transfer outer roller 118 is disposed, facing the secondary transfer inner roller 113.

The fixing unit 12 includes a fixing roller pair 12a, and a pre-fixing conveyance portion 145 that conveys a sheet to a nip of the fixing roller pair 12a. The feeding unit 13 includes a lift plate 131 and an air feeding portion 132. The lift plate 131 moves up and down in a state where a sheet S is stacked on the lift plate 131, and the air feeding portion 132 feeds the sheet S stacked on the lift plate 131. The air feeding portion 132 separates one sheet from the other stacked on the lift plate 131 by using air; and conveys the uppermost sheet stacked on the lift plate 131, while causing the uppermost sheet to stick to the air feeding portion 132 by using air. Note that another feeding portion, such as a roller or a belt, may be used instead of the air feeding portion 132.

Next, an image forming operation of the printer 1 configured in this manner will be described. When an image signal is sent to the exposure apparatus 104a from an apparatus, such as a personal computer, a laser beam generated in accordance with the image signal is emitted from the exposure apparatus 104a to the photosensitive drum 101a of the process cartridge 10Y, and the photosensitive drum 101a is irradiated with the laser beam.

Since the surface of the photosensitive drum 101a is uniformly charged in advance by the charging roller so as to have a predetermined polarity and potential, an electrostatic latent image is formed on the surface of the photosensitive drum 101a when the surface is irradiated with the laser beam emitted from the exposure apparatus 104a to the photosensitive drum 101a via a mirror 105a. The electrostatic latent image formed on the photosensitive drum 101a is developed by the development unit 102a, and a yellow (Y) toner image is formed on the photosensitive drum 101a.

Similarly, photosensitive drums of the process cartridges 10M, 10C, and 10Bk are also irradiated with laser beams emitted from the exposure apparatuses 104b, 104c, and 104d; and magenta (M), cyan (C), and black (Bk) toner images are formed on the photosensitive drums. The toner images formed on the photosensitive drums are transferred onto the intermediate transfer belt 111 by the primary transfer rollers 112a, 112b, 112c, and 112d. Then the full-color toner image is conveyed to a secondary transfer nip T2 formed by the secondary transfer inner roller 113 and the secondary transfer outer roller 118, by the intermediate transfer belt 111 rotated by the driving roller 115. The toner left on the photosensitive drum 101a is collected by the cleaner 103a. Note that the image forming process for each color is performed at a timing at which a corresponding toner image is transferred onto another toner image which has been primary-transferred onto the intermediate transfer belt 111 at a position located upstream of the position at which the corresponding toner image is transferred.

In parallel with the above-described image forming process, the sheet S is fed from the feeding unit 13 in the printer 1. The sheet S is conveyed to the registration unit 144 by the conveyance unit 141 in a sheet conveyance direction indicated by an arrow C (hereinafter, the sheet conveyance direction is indicated by the arrow C). The registration unit 144 corrects the skew of the sheet S, and conveys the sheet S to the secondary transfer nip T2, which serves as an image forming portion, at a predetermined conveyance timing. Then a full-color toner image on the intermediate transfer belt 111 is transferred onto a first sheet surface (front surface) of the sheet S by a secondary transfer bias applied to the secondary transfer outer roller 118. The residual toner left on the intermediate transfer belt 111 is collected by a belt cleaner 114.

The sheet S onto which the toner image has been transferred is conveyed to the fixing roller pair 12a by the pre-fixing conveyance portion 145. The sheet S is then applied with predetermined heat and pressure by the fixing roller pair 12a, and thereby the toner is melted and solidified (fixed). The sheet S having passed through the fixing unit 12 is conveyed to the branch-and-conveyance unit 146, and the branch-and-conveyance unit 146 selects a path of the sheet S from a first discharging path 150a and a second discharging path 150b.

In a case where an image is formed on only one side of the sheet S, the sheet S is conveyed from the branch-and-conveyance unit 146 to the first discharging path 150a, and is discharged to the discharging tray 148 that serves as a first tray.

In a case where images are formed on both sides of the sheet S, the sheet S is conveyed to the second discharging path 150b by the branch-and-conveyance unit 146. The sheet S having been conveyed to the second discharging path 150b is conveyed to a guide member 151, and the guide member 151 selects a path of the sheet S from an escape path 151a and a reversing path 151b. The sheet S having been guided to the escape path 151a by the guide member 151 is discharged to the escape tray 152 that serves as a second tray. For example, if the sheet S cannot be used as a product due to image defect or the like, the sheet S is discharged to the escape tray 152.

The sheet S having been conveyed to the reversing path 151b is conveyed to the reverse conveyance unit 147, and is switch-backed by the reverse conveyance unit 147. The sheet S having been switch-backed is conveyed from the reverse conveyance unit 147 to the duplex conveyance unit 149, and is guided to the conveyance unit 141. After that, an image is formed on a second sheet surface (back surface) of the sheet S in the secondary transfer nip T2, and the sheet S is discharged to the discharging tray 148.

Registration Unit

Next, the registration unit 144 will be described with reference to FIG. 2. The registration unit 144 includes a conveyance roller portion 201, an obliquely-conveying roller portion 205, a registration roller pair 207, a reference member 204 that serves as an abutment member, a CIS 202, a conveyance sensor 203, and a pre-registration sensor 206. The CIS 202 is a contact image sensor.

The conveyance roller portion 201 serves as a conveyance roller and a first conveyance roller, and includes a plurality of (three in the first embodiment) conveyance roller pairs 201a, 201b, and 201c. The conveyance roller pairs 201a to 201c are disposed side by side in the sheet conveyance direction C, and have an identical configuration. For example, the conveyance roller pair 201a includes a rotary shaft 211a, a driving roller 212a, and a driven roller 213a (see FIG. 1). The rotary shaft 211a extends in a width direction W, and serves as a first rotary shaft. The driving roller 212a is rotatably supported by the rotary shaft 211a, and serves as a first rotary member. The driven roller 213a faces the driving roller 212a. The width direction W is an axial direction, and is orthogonal to the sheet conveyance direction C. In the conveyance roller pair 201a, the driven roller 213a can be brought into pressure contact with and separated from the driving roller 212a, so that the state of the conveyance roller pair 201a can be switched between a nip state in which the sheet S is nipped and a nip cancellation state in which the sheet S is not nipped.

The CIS 202 serves as a sheet side-edge detection portion, and is disposed between the conveyance roller pair 201b and the conveyance roller pair 201c in the sheet conveyance direction C. In addition, the CIS 202 is disposed on the reference member 204 side in the width direction W, with respect to a center line CCP of the conveyance path through which the sheet S passes. The CIS 202 detects the position of an edge portion of the sheet S in the width direction W, and changes the output value in accordance with the position of the edge portion of the sheet S. Thus, the CIS 202 can measure the relative distance between the sheet S and the reference member 204, regardless of variations of cutting processes performed in the paper-sheet width direction. Note that the arrangement of the CIS 202 is not limited to the above-described arrangement. In addition, the CIS 202 may not be a contact image sensor. For example, the CIS 202 may be one of various sensors including contact-type sensors and noncontact-type sensors. In another case, a flag sensor or a transmissive or reflective photo sensor may be used instead of the CIS 202.

The conveyance sensor 203 is disposed downstream of the conveyance roller pair 201c and upstream of the obliquely-conveying roller pair 205a in the sheet conveyance direction C, and on the center line CCP. The conveyance sensor 203 is a photo sensor that includes a light emitting portion and a light receiving portion. Thus, the conveyance sensor 203 detects a passage timing of the sheet S by the light receiving portion receiving the light emitted by the light emitting portion and reflected by the sheet S.

The reference member 204 is disposed downstream of the conveyance sensor 203 in the sheet conveyance direction C. In addition, the reference member 204 is disposed in a position in which a reference surface 204a that serves as an abutment surface extends along a side edge portion Sa (see FIG. 5) of the sheet S. The side edge portion Sa is an edge portion of the sheet S in the width direction W.

The obliquely-conveying roller portion 205 is disposed downstream of the conveyance roller portion 201 in the sheet conveyance direction C and in the vicinity of the reference member 204, and includes a plurality of (three in the first embodiment) obliquely-conveying roller pairs 205a, 205b, and 205c. The obliquely-conveying roller pairs 205a to 205c are disposed side by side in the sheet conveyance direction C, and have an identical configuration. For example, the obliquely-conveying roller pair 205a includes a rotary shaft 221a that serves as a second rotary shaft. Because the obliquely-conveying roller pair 205a is inclined by an angle of θ with respect to the reference surface 204a of the reference member 204 disposed in parallel with the sheet conveyance direction C, the rotary shaft 221a extends in a direction that crosses the sheet conveyance direction C and the width direction W. In addition, the obliquely-conveying roller pair 205a includes a driving roller 222a that serves as a second rotary member. The driving roller 222a is rotatably supported by the rotary shaft 221a, and is driven by an obliquely-conveying driving motor 34a (see FIG. 3). In addition, the obliquely-conveying roller pair 205a includes a driven roller 223a (see FIG. 1) that faces the driving roller 222a. In the obliquely-conveying roller pair 205a, the driven roller 223a can be brought into pressure contact with and separated from the driving roller 222a, so that the state of the obliquely-conveying roller pair 205a can be switched between a nip state in which the sheet S is nipped and a nip cancellation state in which the sheet S is not nipped.

Since the rotary shafts are inclined by the angle of θ with respect to the reference surface 204a, the obliquely-conveying roller portion 205 can apply conveyance force that has a component obtained in the sheet conveyance direction C and a component obtained in the width direction W, in which the sheet S abuts against the reference surface 204a. The skew of the sheet S is corrected by the side edge portion of the sheet S abutting against the reference surface 204a. The side edge portion of the sheet S is an edge portion of the sheet S in the width direction W.

The pre-registration sensor 206 serves as a sheet downstream-edge detection portion; and is disposed downstream of the obliquely-conveying roller pair 205c and upstream of the registration roller pair 207 in the sheet conveyance direction C, and on the center line CCP. The pre-registration sensor 206 is a photo sensor that is substantially the same as the conveyance sensor 203, and detects a passage timing of the sheet S by the light receiving portion receiving the light emitted by the light emitting portion and reflected by the sheet S.

The registration roller pair 207 includes a driving roller and a driven roller. The registration roller pair 207 moves in the width direction W while nipping the sheet S; and thereby positions the sheet S in the width direction W, in accordance with the position of a toner image formed on the intermediate transfer belt 111. The registration roller pair 207 that serves as a second conveyance roller conveys the sheet S after positioning the sheet S in the width direction W.

Control Block

Next, control blocks of the printer 1 will be described with reference to FIG. 3. As illustrated in FIG. 3, the printer 1 includes a controller 31 that serves as a controller. The controller 31 includes a CPU 31a, a ROM 31b, a RAM 31c, and a timer 31d. The CPU 31a reads various programs stored in the ROM 31b, and controls each portion of the printer 1. The RAM 31c is used as a work area of the CPU 31a. The timer 31d measures time.

The controller 31 is connected with the CIS 202, the conveyance sensor 203, the pre-registration sensor 206, conveyance driving motors 32a, 32b, and 32c, and conveyance attachment-and-detachment units 33a, 33b, and 33c. In addition, the controller 31 is connected with obliquely-conveying driving motors 34a, 34b, and 34c, obliquely-conveying attachment-and-detachment units 35a, 35b, and 35c, a registration-roller driving motor 36, and a switching motor 37. The controller 31 controls the conveyance force of the obliquely-conveying roller portion 205, in accordance with a detection result from the CIS 202. The control performed by the controller 31 will be more specifically described below.

The conveyance driving motors 32a, 32b, and 32c respectively drive the conveyance roller pairs 201a, 201b, and 201c. Each of the conveyance attachment-and-detachment units 33a, 33b, and 33c serves as a conveyance-rollers-nip switching unit. Specifically, the conveyance attachment-and-detachment unit 33a moves one or both rollers of the conveyance roller pair 201a in a direction in which both of the rollers abut against or are separated from each other. Similarly, the conveyance attachment-and-detachment unit 33b moves one or both rollers of the conveyance roller pair 201b in a direction in which both of the rollers abut against or are separated from each other, and the conveyance attachment-and-detachment unit 33c moves one or both rollers of the conveyance roller pair 201c in a direction in which both of the rollers abut against or are separated from each other. In the registration unit 144 of the first embodiment, the driven rollers of the conveyance roller pairs 201a, 201b, and 201c are brought into contact with and separated from the respective driving rollers.

The obliquely-conveying driving motors 34a, 34b, and 34c respectively drive the obliquely-conveying roller pairs 205a, 205b, and 205c. Each of the obliquely-conveying attachment-and-detachment unit 35a, 35b, and 35c serves as an obliquely-conveying-rollers-nip switching unit. Specifically, the obliquely-conveying attachment-and-detachment unit 35a moves one or both rollers of the obliquely-conveying roller pair 205a in a direction in which both of the rollers abut against or are separated from each other. Similarly, the obliquely-conveying attachment-and-detachment unit 35b moves one or both rollers of the obliquely-conveying roller pair 205b in a direction in which both of the rollers abut against or are separated from each other, and the conveyance attachment-and-detachment unit 35c moves one or both rollers of the obliquely-conveying roller pair 205c in a direction in which both of the rollers abut against or are separated from each other. In the registration unit 144 of the present embodiment, the driven rollers of the obliquely-conveying roller pairs 205a, 205b, and 205c are brought into contact with and separated from the respective driving rollers.

The registration-roller driving motor 36 drives the registration roller pair 207. The switching motor 37 swings the guide member 151, so that the conveyance path of the sheet S is switched between the escape path 151a and the reversing path 151b.

Abutment Operation of Sheet

Next, with reference to a flowchart of FIG. 4, an abutment operation of the registration unit 144 of the first embodiment, in which the sheet S is abutted against the reference surface 204a, will be described. In the abutment operation, the sheet S is conveyed by the obliquely-conveying roller portion 205, so that the side edge portion Sa (see FIG. 5) of the sheet S abuts against the reference surface 204a.

First, as illustrated in FIG. 4, the controller 31 switches the state of the obliquely-conveying roller portion 205 to a non-nip state (S1). In this process, the controller 31 causes the obliquely-conveying attachment-and-detachment units 35a to 35c to switch the state of the obliquely-conveying roller portion 205 to the non-nip state, and thereby causes the obliquely-conveying roller portion 205 to stand by in a state where the nip of the obliquely-conveying roller portion 205 is released. Then the controller 31 switches the state of the conveyance roller portion 201 to a nip state (S2). In this process, the controller 31 causes the conveyance attachment-and-detachment units 33a to 33c to switch the state of the conveyance roller portion 201 to the nip state, and thereby causes the conveyance roller portion 201 to stand by in a state where the nip of the conveyance roller portion 201 is formed.

Then the controller 31 causes the conveyance roller portion 201 to start to convey the sheet S (S3). In this process, as illustrated in FIG. 5, the controller 31 causes the conveyance driving motors 32a to 32c to drive the conveyance roller pairs 201a to 201c in the nip state, for conveying the sheet S.

Then the controller 31 determines whether a predetermined time α has elapsed since the conveyance sensor 203 detected a leading edge Sb of the sheet S that is an edge portion of the sheet S on the downstream side in the sheet conveyance direction C (S4). As illustrated in FIG. 6, in the registration unit 144, when the predetermined time α has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S, the sheet S reaches the obliquely-conveying roller pair 205a. The controller 31 causes the timer 31d to start to measure time when the conveyance sensor 203 detects the leading edge Sb of the sheet S. If the controller 31 determines that the predetermined time α has not elapsed (S4 No), then the controller 31 returns to Step S3. Then the controller 31 repeats the steps S3 and S4 and causes the conveyance roller portion 201 to continue to convey the sheet S until the predetermined time α has elapsed.

If the controller 31 determines that the predetermined time α has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S (S4 Yes), then the controller 31 determines that the sheet S has been conveyed to the obliquely-conveying roller portion 205 by the conveyance roller portion 201. Then the controller 31 causes the obliquely-conveying attachment-and-detachment units 35a to 35c to switch the state of the obliquely-conveying roller portion 205 to the nip state (S5). After that, since the controller 31 is to cause the obliquely-conveying roller portion 205 to start to convey the sheet S, the controller 31 causes the conveyance attachment-and-detachment units 33a to 33c to switch the state of the conveyance roller portion 201 to the non-nip state (S6). Then the controller 31 causes the obliquely-conveying roller portion 205 to convey the sheet S, by driving the obliquely-conveying driving motors 34a to 34c (S7).

In the registration unit 144, in the steps S5 to S7, the oblique conveyance of the sheet S is started by the obliquely-conveying roller portion 205, and the skew of the sheet S and the position of the sheet S in the width direction W are corrected as the sheet is conveyed obliquely. In addition, in the steps S5 and S7, the controller 31 controls the obliquely-conveying roller portion 205 so that the rotational speed and the nip pressure of the obliquely-conveying roller portion 205 are controlled at a first rotational speed and a first pressure, which are preset for each type of the sheet S. In this manner, the controller 31 controls the conveyance force of the obliquely-conveying roller portion 205 at a first conveyance force, and causes the obliquely-conveying roller portion 205 to convey the sheet S.

Then the controller 31 determines whether a predetermined time β has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S (S8). If the controller 31 determines, in this process, that the predetermined time β has not elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S (S8 No), then the controller 31 repeats Step S8 and causes the obliquely-conveying roller portion 205 to continue to convey the sheet S until the predetermined time β has elapsed.

On the other hand, if the controller 31 determines that the predetermined time β has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S (S8 Yes), then the controller 31 determines whether the position of the side edge portion Sa of the sheet S detected by the CIS 202 is within a predetermined range L at the position of the CIS 202 (S9).

FIG. 7 illustrates a case in which the position of the side edge portion Sa of the sheet S is within the predetermined range L, in Step S9, at the position of the CIS 202. For example, the predetermined range L illustrated in FIG. 7 is ±0.3 mm with respect to the position of the reference surface 204a in the width direction W. If the predetermined time β has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S, and the position of the side edge portion Sa of the sheet S is within the predetermined range L determined with respect to the reference surface 204a, the controller 31 determines that the sheet S has a small conveyance resistance and is being conveyed without delay. In this case, the controller 31 does not change the rotational speed of the obliquely-conveying roller portion 205; and executes normal control under which the conveyance force of the obliquely-conveying roller portion 205, which is set in Step S7, is kept.

FIG. 8 is a diagram illustrating a case in which the abutment operation is continued in a state where the conveyance force of the obliquely-conveying roller portion 205, which is set in Step S7, is kept. As illustrated in FIG. 8, in the registration unit 144, since the conveyance by the obliquely-conveying roller portion 205 is continued, the side edge portion Sa and the reference surface 204a contact each other before the leading edge Sb of the sheet S reaches the pre-registration sensor 206. In this manner, the skew of the sheet S and the position of the sheet S in the width direction W are corrected in the registration unit 144. After that, in the registration unit 144, the sheet S is conveyed, while the side edge portion Sa of the sheet S slides on the reference surface 204a, until the leading edge Sb of the sheet S reaches the registration roller pair 207.

As described above, the controller 31 determines whether the position of the side edge portion Sa of the sheet S is within the predetermined range L, when the predetermined time β has elapsed, following the predetermined time α, since the conveyance sensor 203 detected the leading edge Sb of the sheet S. In the registration unit 144, if the sheet S is skewed significantly, the position of the side edge portion Sa of the sheet S may be out of the predetermined range L when the predetermined time β has elapsed, even if the position of the side edge portion Sa is within the predetermined range L when the predetermined time α has elapsed. In such a case, in the registration unit 144, if the abutment operation is continued without changing the conveyance force of the obliquely-conveying roller portion 205, the abutment operation may not be completed before the sheet S reaches the registration roller pair 207.

However, in the steps S8, S9 and S10, the controller 31 can prevent such a case in which the abutment operation is not completed before the sheet S reaches the registration roller pair 207. Thus, the controller 31 can suppress failure in conveyance of sheets and image defect, which are caused by the uncompleted abutment operation. The predetermined time β is a predetermined time (first time) of the first embodiment.

If the controller 31 determines in Step S9 that the position of the side edge portion Sa of the sheet S is not within the predetermined range L at the position of the CIS 202 (S9 No), then the controller 31 determines that the Sheet S has a large conveyance resistance and is being conveyed with delay. FIG. 9 illustrates a case in which the controller 31 determines in Step S9 that the position of the side edge portion Sa of the sheet S is not within the predetermined range L (that is, out of the predetermined range L) at the position of the CIS 202. In such a case, since the conveyance delay of the sheet S is not eliminated even if the normal control is continued, the controller 31 executes recovery control and changes the conveyance force of the obliquely-conveying roller portion 205, for eliminating the conveyance delay. In the recovery control, the controller 31 of the first embodiment increases the conveyance speed of the sheet S by changing the rotational speed of the obliquely-conveying roller portion 205 from the first rotational speed to a second rotational speed, by increasing the rotational speed of the obliquely-conveying driving motors 34a to 34c (S10).

In this manner, the controller 31 changes the conveyance force of the obliquely-conveying roller portion 205 to a second conveyance force larger than the first conveyance force, which is set in the steps S5 and S7. As a result, the sheet S can be conveyed downstream in the sheet conveyance direction C, without conveyance delay.

The controller 31 proceeds to Step S11 after Step S10 or if the controller 31 determines in Step S9 that the position of the side edge portion Sa of the sheet S is within the predetermined range L at the position of the CIS 202 (S9 Yes). In Step S11, the controller 31 determines whether a predetermined time γ has elapsed since the pre-registration sensor 206 detected the leading edge Sb of the sheet S (S11). The predetermined time γ is a second time. If the controller 31 determines, in this process, that the predetermined time γ has not elapsed since the pre-registration sensor 206 detected the leading edge Sb of the sheet S (S11 No), then the controller 31 repeats Step S11 and causes the obliquely-conveying roller portion 205 to continue to convey the sheet S until the predetermined time γ has elapsed.

If the controller 31 determines that the predetermined time γ has elapsed since the pre-registration sensor 206 detected the leading edge Sb of the sheet S (S11 Yes), then the controller 31 determines that the sheet S has been conveyed to the registration roller pair 207 by the obliquely-conveying roller portion 205. Then the controller 31 causes the registration roller pair 207 to convey the sheet S, by driving the registration-roller driving motor 36 (S12). After that, the controller 31 causes the obliquely-conveying attachment-and-detachment units 35a to 35c to switch the state of the obliquely-conveying roller portion 205 to the non-nip state (S13), and causes the registration roller pair 207 to convey the sheet S to the secondary transfer portion located downstream of the registration unit 144 in the sheet conveyance direction C.

FIG. 10 illustrates a state in which the conveyance of the sheet S is started by the registration roller pair 207 in a state where the abutment operation is completed. When the controller 31 causes the registration roller pair 207 to convey the sheet S in the sheet conveyance direction C, the controller 31 switches the state of the obliquely-conveying roller portion 205 to the non-nip state for preventing the component of the conveyance force of the obliquely-conveying roller portion 205 obtained in the width direction W, from affecting the conveyance of the sheet S.

Note that in the registration unit 144, if the sheet S is skewed significantly and the sheet S has a large conveyance resistance, the position of the side edge portion Sa of the sheet S may not be within the predetermined range L at the position of the CIS 202 before the leading edge Sb of the sheet S reaches the pre-registration sensor 206. In this case, the controller 31 determines that the abutment operation will not be completed before the leading edge Sb of the sheet S reaches the registration roller pair 207, and stops the conveyance of the sheet S for preventing image defect, such as misalignment of printing. In addition, the controller 31 causes an informing unit (not illustrated) to inform a user that the image defect (misalignment of printing) may be occurring due to the uncompleted abutment operation, that the conveyance of the sheet is being stopped, and that the sheet left in the printer 1 needs to be removed.

Output Value from CIS

FIG. 11 is a graph illustrating the output value from the CIS 202 that changes with time, and that is obtained when the normal control is performed by the controller 31. The horizontal axis represents the time, and the vertical axis represents the output value from the CIS 202. The predetermined times α, β, and γ indicated along the horizontal axis are measured by the timer 31d. The sheet S is first conveyed by the conveyance roller portion 201 (conveyance-roller-pair conveyance period, see Step S3), and then is conveyed by the obliquely-conveying roller portion 205 (obliquely-conveying-roller-pair conveyance period, see Step S7). As the sheet S is conveyed by the obliquely-conveying roller portion 205, the position (hereinafter referred to as a detection position) of the side edge portion Sa detected by the CIS 202 gradually approaches the position (hereinafter referred to as a reference position) of the reference surface 204a of the reference member 204 in the width direction W.

If the detection position is within the predetermined range L when the predetermined time β has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S, the controller 31 continues to perform the normal control. Since the normal control is continued, the side edge portion Sa of the sheet S abuts against the reference surface 204a and the oblique conveyance is completed before the pre-registration sensor 206 detects the leading edge Sb of the sheet S. When the oblique conveyance is completed, the oblique-conveyance period ends. After that, the sheet S is conveyed while the side edge portion Sa of the sheet S slides on the reference surface 204a, so that the detection position is kept at the reference position (reference-member slide-and-conveyance period).

When the predetermined time γ has elapsed since the pre-registration sensor 206 detected the leading edge Sb of the sheet S, the controller 31 causes the obliquely-conveying roller portion 205 to end the conveyance of the sheet S (that is, the obliquely-conveying-roller-pair conveyance period ends). Then the controller 31 causes the registration roller pair 207 to start the conveyance of the sheet S (that is, the registration-roller-pair conveyance period starts).

FIG. 12 is a graph illustrating the output value from the CIS 202 that changes with time, and that is obtained when the recovery control is performed by the controller 31. The horizontal axis represents the time, and the vertical axis represents the output value from the CIS 202. The sheet S is first conveyed by the conveyance roller portion 201 (conveyance-roller-pair conveyance period, see Step S3), and then is conveyed by the obliquely-conveying roller portion 205 (oblique-conveyance period, see Step S7). As the sheet S is conveyed by the obliquely-conveying roller portion 205, the position (hereinafter referred to as a detection position) of the side edge portion Sa detected by the CIS 202 gradually approaches the position (hereinafter referred to as a reference position) of the reference surface 204a of the reference member 204 in the width direction W.

If the detection position is out of the predetermined range L when the predetermined time β has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S (Step S9: No), the controller 31 executes the recovery control. In the recovery control, the controller 31 increases the rotational speed of the obliquely-conveying roller portion 205 (see Step S10). Since the recovery control is executed, the speed at which the detection position approaches the reference position increases, and the side edge portion Sa abuts against the reference surface 204a and the oblique conveyance is completed before the pre-registration sensor 206 detects the leading edge Sb of the sheet S. After that, the sheet S is conveyed while the side edge portion Sa of the sheet S slides on the reference surface 204a, so that the detection position is kept at the reference position (reference-member slide-and-conveyance period).

When the predetermined time γ has elapsed since the pre-registration sensor 206 detected the leading edge Sb of the sheet S, the controller 31 causes the obliquely-conveying roller portion 205 to end the conveyance of the sheet S (that is, the obliquely-conveying-roller-pair conveyance period ends). Then the controller 31 causes the registration roller pair 207 to start the conveyance of the sheet S (that is, the registration-roller-pair conveyance period starts). Summary of First Embodiment

As described above, in the abutment operation in which the sheet S is abutted against the reference surface 204a by the obliquely-conveying roller portion 205, the registration unit 144 of the first embodiment is controlled such that the conveyance force of the obliquely-conveying roller portion 205 is controlled at the first conveyance force until the predetermined time β has elapsed. In addition, if the predetermined time β has elapsed, and the position of the side edge portion Sa detected by the CIS 202 is out of the predetermined range L, the registration unit 144 is controlled such that the conveyance force of the obliquely-conveying roller portion 205 is controlled at the second conveyance force larger than the first conveyance force, by increasing the rotational speed of the obliquely-conveying roller portion 205. As a result, even if the sheet S has a large conveyance resistance and the conveyance delay occurs in the skew correction of the sheet S, the registration unit 144 can quickly complete the abutment operation and prevent the productivity from being lowered in the skew correction of the sheet S.

Second Embodiment

Next, a registration unit 144 of a second embodiment will be described. The registration unit 144 of the second embodiment changes the conveyance force of the obliquely-conveying roller portion 205 in the recovery control, by increasing the nip pressure of the obliquely-conveying roller portion 205, without changing the rotational speed of the obliquely-conveying roller portion 205. The registration unit 144 of the second embodiment differs from the registration unit 144 of the above-described first embodiment in this point. Since the other configuration of the second embodiment is the same as that of the first embodiment, a component identical to that of the first embodiment is given an identical symbol, a process identical to that of the first embodiment is given an identical step number, and the description thereof will be omitted.

With reference to a flowchart of FIG. 13, an abutment operation of the registration unit 144 of the second embodiment, in which the sheet S is abutted against the reference surface 204a, will be described. If the controller 31 determines that the predetermined time α has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S (S4 Yes), then the controller 31 determines that the sheet S has been conveyed to the obliquely-conveying roller portion 205 by the conveyance roller portion 201. Then the controller 31 causes the obliquely-conveying attachment-and-detachment units 35a to 35c, which serves as a nip-pressure adjustment portion, to switch the state of the obliquely-conveying roller portion 205 to a weak nip state (S21). In the weak nip state, the nip pressure of the obliquely-conveying roller portion 205 is controlled at a first pressure.

In the registration unit 144, in the steps S6, S7, and S21, the oblique conveyance of the sheet S is started by the obliquely-conveying roller portion 205, and the skew of the sheet S and the position of the sheet S in the width direction W are corrected as the sheet is conveyed obliquely. In addition, in the steps S7 and S21, the controller 31 controls the obliquely-conveying roller portion 205 so that the rotational speed and the nip pressure of the obliquely-conveying roller portion 205 are controlled at a first rotational speed and a first pressure, which are preset for each type of the sheet S. Thus, the controller 31 controls the conveyance force of the obliquely-conveying roller portion 205 at a first conveyance force, and causes the obliquely-conveying roller portion 205 to convey the sheet S.

If the controller 31 determines in Step S9 that the position of the side edge portion Sa of the sheet S is not within the predetermined range L at the position of the CIS 202 (S9 No), then the controller 31 determines that the sheet S has a large conveyance resistance and is being conveyed with delay. In this case, since the conveyance delay of the sheet S is not eliminated even if the normal control is continued, the controller 31 executes recovery control and changes the conveyance force of the obliquely-conveying roller portion 205, for eliminating the conveyance delay. In the recovery control, the controller 31 of the second embodiment increases the conveyance speed of the sheet S by switching the state of the obliquely-conveying roller portion 205 to a strong nip state, by causing the obliquely-conveying attachment-and-detachment units 35a to 35c to increase the nip pressure of the obliquely-conveying roller portion 205 from the first pressure to a second pressure higher than the first pressure (S22).

In this manner, the controller 31 changes the conveyance force of the obliquely-conveying roller portion 205 to a second conveyance force larger than the first conveyance force, which is set in the steps S7 and S21. As a result, the sheet S can be conveyed downstream in the sheet conveyance direction C, without conveyance delay.

As described above, in the abutment operation of the obliquely-conveying roller portion 205 in which the sheet S is abutted against the reference surface 204a, the registration unit 144 of the second embodiment is controlled such that the conveyance force of the obliquely-conveying roller portion 205 is controlled at the first conveyance force until the predetermined time β has elapsed. In addition, if the predetermined time β has elapsed, and the position of the side edge portion Sa detected by the CIS 202 is out of the predetermined range L, the registration unit 144 is controlled such that the conveyance force of the obliquely-conveying roller portion 205 is controlled at the second conveyance force larger than the first conveyance force, by increasing the nip pressure of the obliquely-conveying roller portion 205. As a result, even if the sheet S has a large conveyance resistance and the conveyance delay occurs in the skew correction of the sheet S, the registration unit 144 can quickly complete the abutment operation and prevent the productivity from being lowered in the skew correction of the sheet S.

Third Embodiment

Next, a registration unit 144 of a third embodiment will be described. The registration unit 144 of the third embodiment changes the conveyance force of the obliquely-conveying roller portion 205 in the recovery control, by increasing the rotational speed and the nip pressure of the obliquely-conveying roller portion 205. The registration unit 144 of the third embodiment differs from the registration unit 144 of the above-described first embodiment and the registration unit 144 of the above-described second embodiment in this point. Since the other configuration of the third embodiment is the same as that of the first and the second embodiments, a component identical to that of the first and the second embodiments is given an identical symbol, a process identical to that of the first and the second embodiments is given an identical step number, and the description thereof will be omitted.

With reference to a flowchart of FIG. 14, an abutment operation of the registration unit 144 of the third embodiment, in which the sheet S is abutted against the reference surface 204a, will be described. If the controller 31 determines in Step S9 that the position of the side edge portion Sa of the sheet S is not within the predetermined range L at the position of the CIS 202 (S9 No), then the controller 31 determines that the sheet S has a large conveyance resistance and is being conveyed with delay. In this case, since the conveyance delay of the sheet S is not eliminated even if the normal control is continued, the controller 31 executes recovery control and changes the conveyance force of the obliquely-conveying roller portion 205, for eliminating the conveyance delay.

In the recovery control, the controller 31 of the third embodiment increases the rotational speed of the obliquely-conveying roller portion 205 from the first rotational speed to the second rotational speed, by increasing the rotational speed of the obliquely-conveying driving motors 34a to 34c. In addition, in the recovery control, the controller 31 switches the state of the obliquely-conveying roller portion 205 to the strong nip state, by causing the obliquely-conveying attachment-and-detachment units 35a to 35c to increase the nip pressure of the obliquely-conveying roller portion 205 from the first pressure to the second pressure higher than the first pressure. That is, the controller 31 increases the conveyance speed of the sheet S by increasing the rotational speed and the nip pressure of the obliquely-conveying roller portion 205 (S31).

In this manner, the controller 31 changes the conveyance force of the obliquely-conveying roller portion 205 to the second conveyance force larger than the first conveyance force, which is set in the steps S7 and S21. As a result, the sheet S can be conveyed downstream in the sheet conveyance direction C, without conveyance delay.

As described above, in the abutment operation in which the sheet S is abutted against the reference surface 204a by the obliquely-conveying roller portion 205, the registration unit 144 of the third embodiment is controlled such that the conveyance force of the obliquely-conveying roller portion 205 is controlled at the first conveyance force until the predetermined time β has elapsed. In addition, in the registration unit 144, if the predetermined time β has elapsed, and the position of the side edge portion Sa detected by the CIS 202 is out of the predetermined range L, the rotational speed and the nip pressure of the obliquely-conveying roller portion 205 are increased. In this manner, in the registration unit 144, the conveyance force is controlled at the second conveyance force larger than the first conveyance force. As a result, even if the sheet S has a large conveyance resistance and the conveyance delay occurs in the skew correction of the sheet S, the registration unit 144 can quickly complete the abutment operation and prevent the productivity from being lowered in the skew correction of the sheet S. Modifications

Note that in the first to the third embodiments, the conveyance of the sheet S is stopped if the abutment operation of the sheet S is not completed before the leading edge Sb of the sheet S reaches the registration roller pair 207. However, the present disclosure is not limited to this. For example, if the abutment operation of the sheet S is not completed before the leading edge Sb of the sheet S reaches the registration roller pair 207, the controller 31 may cause the switching motor 37 to drive the guide member 151. In this case, the sheet S may be discharged to the escape tray 152 through the escape path 151a.

In this configuration, even if the abutment operation is not completed before the leading edge Sb of the sheet S reaches the registration roller pair 207, the registration unit 144 does not stop the conveyance of the sheet S, and thus can prevent the productivity from being lowered. In addition, a user of the printer 1 can distinguish a sheet having a defect in printing, caused by the uncompleted abutment operation, from sheets discharged to the discharging tray 148; and can easily remove the sheet discharged to the escape tray 152. Thus, the usability can be increased.

In addition, although the registration unit 144 causes the obliquely-conveying attachment-and-detachment units 35a to 35c to bring the driven rollers into contact with the driving rollers and separate the driven rollers from the driving rollers in the first to the third embodiments, the present disclosure is not limited to this. For example, the registration unit 144 may cause the obliquely-conveying attachment-and-detachment units 35a to 35c to bring the driving rollers into contact with the driven rollers and separate the driving rollers from the driven rollers.

In addition, in the first to the third embodiments, the predetermined range L is, for example, ±0.3 mm with respect to the position of the reference surface 204a in the width direction W. However, the present disclosure is not limited to this. The predetermined range L may be set in advance, as appropriate, in accordance with desired print precision or a sheet size, or may be set by a user.

In addition, in the first to the third embodiments, the controller 31 determines whether the position of the side edge portion Sa of the sheet S is within the predetermined range L at the position of the CIS 202, when the predetermined time β has elapsed since the conveyance sensor 203 detected the leading edge Sb of the sheet S. However, the operation of the controller 31 is not limited to this. For example, the controller 31 may cause the timer 31d to start to measure time when the conveyance of the sheet S is started by the obliquely-conveying roller portion 205. In this case, when a predetermined time has elapsed since the conveyance of the sheet S was started by the obliquely-conveying roller portion 205 and the timer 31d started to measure time, the controller 31 may determine whether the position of the side edge portion Sa of the sheet S is within the predetermined range L at the position of the CIS 202.

In addition, in the first to the third embodiments, the obliquely-conveying roller portion 205 is disposed in front of the secondary transfer nip T2. However, the present disclosure is not limited to this. For example, the obliquely-conveying roller portion 205 may be disposed in the duplex conveyance unit 149 or another apparatus located downstream of the printer 1 and connected to the printer 1, and the present invention may be applied to such a configuration.

In addition, in the first to the third embodiments, the conveyance roller portion 201 includes the three conveyance roller pairs, and the obliquely-conveying roller portion 205 includes the three obliquely-conveying roller pairs. However, the number of the roller pairs is not limited to a particular number. In addition, the obliquely-conveying roller pairs 205a to 205c are inclined by the identical angle of θ with respect to the sheet conveyance direction C. However, the present disclosure is not limited to this. For example, the obliquely-conveying roller pairs 205a to 205c may be inclined by different angles with respect to the sheet conveyance direction C.

In addition, in the first to the third embodiments, the present invention has been described, for example, for the registration unit 144, which serves as a sheet conveyance apparatus that includes the controller 31. However, the printer 1 may be regarded as a sheet conveyance apparatus.

In addition, in the first to the third embodiments, the description has been made for the electrophotographic printer 1. However, the present invention is not limited to this. For example, the present invention may also be applied to an ink-jet image forming apparatus that forms images on sheets by injecting ink from a nozzle.

The present invention may be embodied by providing a program, which achieves one or more functions of the above-described embodiments, to a system or an apparatus via a network or a storage medium, and by causing one or more processors of the system or the apparatus to read and execute the program. In addition, the present invention may be embodied by a circuit (for example, an ASIC) that achieves one or more functions.

Other Embodiments

Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.

While the present 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.

This application claims the benefit of Japanese Patent Application No. 2021-174829, filed Oct. 26, 2021, which is hereby incorporated by reference herein in its entirety.

Claims

1. A sheet conveyance apparatus comprising:

a conveyance roller configured to convey a sheet;

an abutment member including an abutment surface and configured to correct skew of the sheet, the abutment surface being disposed downstream of the conveyance roller and extending along a sheet conveyance direction, the abutment surface being a surface against which a side edge portion of the sheet in a width direction orthogonal to the sheet conveyance direction abuts;

an obliquely conveying roller disposed downstream of the conveyance roller in the sheet conveyance direction and configured to convey the sheet such that the side edge portion is moved toward the abutment surface;

a sheet side-edge detection portion configured to detect a position of the side edge portion of the sheet in the width direction and change an output value in accordance with the position of the side edge portion of the sheet conveyed by the obliquely conveying roller; and

a controller configured to control conveyance force applied by the obliquely conveying roller in the width direction of the sheet, in accordance with a detection result from the sheet side-edge detection portion,

wherein the controller is configured to control the conveyance force of the obliquely conveying roller at a first conveyance force until a predetermined time has elapsed, in an abutment operation in which the sheet is abutted against the abutment surface by the obliquely conveying roller, and control the conveyance force of the obliquely conveying roller at a second conveyance force larger than the first conveyance force if the predetermined time has elapsed and the position of the side edge portion of the sheet detected by the sheet side-edge detection portion is out of a predetermined range.

2. The sheet conveyance apparatus according to claim 1, wherein the controller is configured to

control rotational speed of the obliquely conveying roller at a first rotational speed if the conveyance force of the obliquely conveying roller is controlled at the first conveyance force, and

control the rotational speed of the obliquely conveying roller at a second rotational speed faster than the first rotational speed if the conveyance force of the obliquely conveying roller is controlled at the second conveyance force.

3. The sheet conveyance apparatus according to claim 1, wherein the obliquely conveying roller includes wherein the controller is configured to

a driving roller configured to rotate, and

a driven roller, the driving roller being configured to drive the driven roller, the driving roller and the driven roller being configured to form a nip and convey a sheet while nipping the sheet in the nip,

control nip pressure of the nip at a first pressure if the conveyance force of the obliquely conveying roller is controlled at the first conveyance force, and

control the nip pressure of the nip at a second pressure higher than the first pressure if the conveyance force of the obliquely conveying roller is controlled at the second conveyance force.

4. The sheet conveyance apparatus according to claim 1, wherein if the predetermined time has elapsed and the position of the side edge portion of the sheet detected by the sheet side-edge detection portion is within the predetermined range, the controller controls the conveyance force of the obliquely conveying roller at the first conveyance force until the abutment operation is completed.

5. The sheet conveyance apparatus according to claim 1, wherein the predetermined time is a first time,

wherein the conveyance roller is a first conveyance roller,

wherein the sheet conveyance apparatus further includes a sheet downstream-edge detection portion disposed downstream of the obliquely conveying roller in the sheet conveyance direction and configured to detect an edge portion of the sheet on a downstream side in the sheet conveyance direction, and a second conveyance roller disposed downstream of the sheet downstream-edge detection portion in the sheet conveyance direction and configured to convey the sheet, and

wherein the controller is configured to cause the second conveyance roller to convey the sheet if a second time has elapsed since the sheet downstream-edge detection portion detected the edge portion of the sheet on the downstream side.

6. The sheet conveyance apparatus according to claim 5, wherein the controller is configured to separate the obliquely conveying roller from the sheet when the controller causes the second conveyance roller to convey the sheet.

7. The sheet conveyance apparatus according to claim 6, wherein the obliquely conveying roller further includes wherein the controller is configured to remove the nip by separating the driven roller from the driving roller when the controller causes the second conveyance roller to convey the sheet.

a driving roller configured to rotate, and

a driven roller, the driving roller being configured to drive the driven roller, the driving roller and the driven roller being configured to form a nip and convey a sheet while nipping the sheet in the nip, and

8. The sheet conveyance apparatus according to claim 5, wherein in a period of time from when the abutment operation is started until when the sheet downstream-edge detection portion detects the edge portion of the sheet on the downstream side, if the position of the side edge portion of the sheet detected by the sheet side-edge detection portion is within the predetermined range, the controller determines that the abutment operation has been completed.

9. The sheet conveyance apparatus according to claim 8, further comprising:

a first tray to which a sheet is discharged; and

a second tray to which a sheet is discharged and which is different from the first tray,

wherein a sheet on which the controller has determined that the abutment operation has been completed is discharged to the first tray, and

wherein a sheet that has reached the second conveyance roller in a state where the controller has determined that the abutment operation has not been completed on the sheet is discharged to the second tray.

10. The sheet conveyance apparatus according to claim 1, further comprising an image forming portion configured to form an image on a sheet.