A roller drive transmission device, comprising:
- a drive input gear including a gear portion to be rotated in a first rotational direction about a predetermined axis by having a rotational drive force input thereto and an engaging portion formed on a side surface of the gear portion;
- a drive transmission gear arranged adjacent to the drive input gear on the axis and slidable along an axial direction of the axis, the drive transmission gear including an engaged portion formed on one side surface in the axial direction and to be engaged with the engaging portion and a first gear portion having first gear teeth formed on the other side surface opposite to the engaged portion;
- a roller unit arranged adjacent to the drive transmission gear on the axis and configured to convey a sheet by being rotated about the axis, the roller unit including a second gear portion having second gear teeth formed on a side surface facing the drive transmission gear and engageable with the first gear teeth;
- and
- a ratchet mechanism configured to couple or decouple the drive input gear and the roller unit with rotation about the axis,
- wherein:
- the ratchet mechanism is configured such that in case the rotational drive force is input to the drive input gear, the drive input gear, the drive transmission gear and the roller unit are integrally rotated in the first rotational direction by the engagement of the first and second gear teeth, the drive input gear rotates in the first rotational direction and the drive transmission gear is slid to a first position close to the roller unit, and that the first and second gear teeth are disengaged, whereby the drive transmission gear is slid to a second position closer to the drive input gear than the first position to decouple the roller unit and the drive transmission gear, in case the input of the rotational drive force to the drive input gear is cut off, the roller unit rotates, following the sheet, and the second gear teeth are rotated in the first rotational direction with respect to the first gear teeth;
- and
- the ratchet mechanism includes a load adjustment mechanism configured to make a rotational load in the first rotational direction of the drive transmission gear arranged at the second position larger than a movement load in the axial direction.