Switchback transport mechanism and image forming apparatus provided therewith

A switchback transport mechanism for switching back a sheet by guiding the sheet from a guiding path to a switchback transport path through a connecting point and then ejecting the sheet from the switchback transport path to the ejecting path through the connecting point, the switchback transport mechanism comprising:

• a first transport section for applying propelling force to a sheet in the guiding path;
• a second transport section for applying propelling force to a sheet in the ejecting path;
• a third transport section including a first roller that has a circumferential surface with a cutout portion and a second roller placed in contact with the circumferential surface of the first roller, the first and second rollers being placed in such a manner as to be selectively attached to and detached from each other, the third transport section selectively applying propelling forces in a frontward direction and a backward direction to a sheet in the switchback transport path through the first and second rollers;
• and
• a transport control section for controlling operations of the first, second, and third transport sections, the transport control section detaching the first and second rollers from each other in a time period when no sheet is being transported by the third transport section, wherein the transport control section:
• guides a sheet into the switchback transport path by rotating the first roller in a forward direction in a first time period between the instant when a tail end of the sheet in the guiding path passes through the first transport section and the instant when the tail end passes through the connecting point;
• ejects the sheet out from the switchback transport path by rotating the first roller in a backward direction in a second time period between the instant when the tail end passes through the connecting point and the instant when the tail end reaches the second transport section;
• and
• brings the first roller to a stop, with the cutout portion facing the second roller, in a third time period other than the first and second time periods.