Sheet processing apparatus and image forming system incorporating the same

1. A sheet processing apparatus comprising:

a roller pair configured to convey at least one sheet;

a first sheet conveyer configured to convey the at least one sheet to the roller pair; and

circuitry configured to cause the first sheet conveyer to butt a leading edge of the at least one sheet to the roller pair, and

cause the roller pair to begin rotating in reverse to align the leading edge of the at least one sheet after the leading edge of the at least one sheet butts the roller pair.

2. The sheet processing apparatus according to claim 1 ,

wherein the circuitry is configured to change, according to a property of the at least one sheet, a reverse rotation amount of the roller pair by which the roller pair rotates in reverse to align the leading edge of the at least one sheet.

3. The sheet processing apparatus according to claim 2 ,

wherein the property of the at least one sheet includes a thickness of the at least one sheet, and

wherein the circuitry is configured to increase the reverse rotation based on the thickness of the at least one sheet.

4. The sheet processing apparatus according to claim 1 , further comprising a second sheet conveyer configured to convey a following sheet subsequent to the at least one sheet,

wherein the circuitry is configured to cause the second sheet conveyer to convey the following sheet such that a leading edge of the following sheet butts the roller pair aligning the leading edge of the following sheet and the leading edge of the at least one sheet.

5. The sheet processing apparatus according to claim 4 ,

wherein the circuitry is configured to cause the roller pair to rotate in reverse to cause the leading edge of the following sheet to butt the roller pair.

6. The sheet processing apparatus according to claim 4 ,

wherein, in response to a number of overlaid sheets reaching a set number, the circuitry is configured to

cause the second sheet conveyer to convey the following sheet such that the leading edge of the following sheet butts the roller pair and the following sheet bends,

cause the first sheet conveyer to convey the at least one sheet such that the leading edge of the at least one sheet butts the roller pair and the at least one sheet bends, and

cause the roller pair to convey and overlay the following sheet and the at least one sheet.

7. The sheet processing apparatus according to claim 6 , wherein the circuitry is configured to cause the roller pair to rotate in response to the following sheet being bent a set amount.

8. The sheet processing apparatus according to claim 4 , wherein the second sheet conveyer includes a widened portion configured to allow a portion of the following sheet to bend at the widened portion.

9. The sheet processing apparatus according to claim 1 , further comprising a sheet bundle processing device disposed downstream from the roller pair in the conveyance direction,

wherein the sheet bundle processing device is configured to process the sheet bundle.

10. An image forming system comprising:

an image forming apparatus configured to form an image on a sheet; and

the sheet processing apparatus according to claim 1 .

11. The sheet processing apparatus according to claim 1 , wherein the first sheet conveyer includes a widened portion configured to allow a portion of the at least one sheet to bend at the widened portion.

12. A sheet processing apparatus comprising:

a roller pair configured to convey at least one sheet;

a first sheet conveyer configured to convey the at least one sheet to the roller pair;

a second sheet conveyer configured to convey a following sheet subsequent to the at least one sheet; and

circuitry configured to

cause the first sheet conveyer to butt a leading edge of the at least one sheet to the roller pair,

cause the roller pair to rotate in reverse to align the leading edge of the at least one sheet in response to the leading edge of the at least one sheet butting against the roller pair, and

cause the second sheet conveyer to convey the following sheet such that a leading edge of the following sheet butts the roller pair aligning the leading edge of the following sheet and the leading edge of the at least one sheet.

13. The sheet processing apparatus according to claim 12 , wherein the circuitry is configured to cause the roller pair to rotate in reverse to cause the leading edge of the following sheet to butt the roller pair.

14. The sheet processing apparatus according to claim 12 , wherein, in response to a number of overlaid sheets reaching a set number, the circuitry is configured to

cause the second sheet conveyer to convey the following sheet such that the leading edge of the following sheet butts the roller pair and the following sheet bends,

cause the first sheet conveyer to convey the at least one sheet such that the leading edges of the at least one sheet butt the roller pair and the at least one sheet bends, and

cause the roller pair to convey and overlay the following sheet and the at least one sheet.

15. The sheet processing apparatus according to claim 14 , wherein the circuitry is configured to cause the roller pair to rotate in response to the following sheet being bent a set amount.

16. The sheet processing apparatus according to claim 12 , further comprising a sheet bundle processing device disposed downstream from the roller pair in the conveyance direction,

wherein the sheet bundle processing device is configured to process the sheet bundle.

17. An image forming system comprising:

an image forming apparatus configured to form an image on a sheet; and

the sheet processing apparatus according to claim 12 .

18. The sheet processing apparatus according to claim 12 , wherein the first sheet conveyer includes a widened portion configured to allow a portion of the at least one sheet to bend at the widened portion.

19. The sheet processing apparatus according to claim 12 , wherein the second sheet conveyer includes a widened portion configured to allow a portion of the following sheet to bend at the widened portion.