Image forming apparatus including sheet bending amount detection unit and sheet speed control

An image forming apparatus comprising:

• a transfer portion configured to convey a sheet while nipping the sheet and transfer a toner image to the sheet;
• a fixing portion configured to convey the sheet while nipping the sheet and fix the toner image transferred by the transfer portion to the sheet;
• a detection unit disposed between the transfer portion and the fixing portion in a sheet conveyance direction and configured to detect a bending amount of the sheet nipped between the transfer portion and the fixing portion;
• and
• a control unit,
• wherein the detection unit includes:
• a first rotation member configured to rotate by being pressed by the sheet nipped by the transfer portion and the fixing portion;
• a second rotation member configured to rotate in a rotation direction from a standby position by being pressed by the first rotation member;
• a rotary encoder configured to output a pulse signal corresponding to a rotation amount of the second rotation member;
• and
• a rotation detector configured to detect that the second rotation member has reached a detection position downstream of the standby position in the rotation direction, and
• the control unit controls a sheet conveyance speed of the fixing portion based on the pulse signal output from the rotary encoder after the rotation detector detects that the second rotation member has reached the detection position.

An image forming apparatus comprising:

• a transfer portion configured to convey a sheet while nipping the sheet and transfer a toner image to the sheet;
• a fixing portion configured to convey the sheet while nipping the sheet and fix the toner image transferred by the transfer portion to the sheet;
• a detection unit disposed between the transfer portion and the fixing portion in a sheet conveyance direction and configured to detect a bending amount of the sheet nipped between the transfer portion and the fixing portion;
• and
• a control unit,
• wherein the detection unit includes:
• one flag configured to rotate in a rotation direction from a standby position by being pressed by the sheet nipped by the transfer portion and the fixing portion, the flag including a first detected portion and a second detected portion;
• a rotary encoder configured to output a pulse signal corresponding to a rotation amount of the flag by detecting the first detected portion;
• and
• a rotation detector configured to detect that the flag has reached a detection position downstream of the standby position in the rotation direction by detecting the second detected portion, and
• the control unit controls a sheet conveyance speed of the fixing portion based on the pulse signal output from the rotary encoder after the rotation detector detects that the flag has reached the detection position.