Patent ID: 7574158

Claim:
A fixing device comprising: a fixing unit including a fixing roller pair for fixing a toner image formed by an image forming unit on a sheet; an openable/closable fixing cover unit for defining a forward transport path for transporting the sheet discharged from the fixing roller pair, and a backward transport path, disposed below the forward transport path, for transporting the sheet discharged from the fixing roller pair to the image forming unit again for forming the toner image on both sides of the sheet; a sheet detection arm having one end thereof extending in the forward transport path, and the other end thereof extending in the backward transport path; a first rotary shaft provided in the fixing cover unit, the first rotary shaft being fixed to a center of pivotal movement of the sheet detection arm, and extending in a direction substantially orthogonal to a transport direction of the sheet; a second rotary shaft provided in the fixing unit, the second rotary shaft being so constructed that a rotation of the first rotary shaft is transmitted by a contact thereof with one end of the first rotary shaft in a state that the fixing cover unit is closed, and that the contact with the one end of the first rotary shaft is released in a state that the fixing cover unit is opened; and a sensor unit, provided in the fixing unit, for detecting whether the sheet is being transported at least in the forward transport path and in the backward transport path in accordance with a rotation of the second rotary shaft transmitted from the first rotary shaft, wherein the sheet detection arm is pivotally moved in such a direction as to retract from the backward transport path in response to an opening of the fixing cover unit.