Patent ID: 8849176

Claim:
An automatic document feeder, comprising: a frame; a cover, wherein an end of the cover is pivoted to the frame and therefore the cover can be opened or closed relative to the frame, and the end of the cover pivoted to frame has a cam; a gear chain disposed in the frame, comprising: a plurality of driven gears, wherein the driven gears disposed with a first axial direction as a rotating axle are engaged with each other; and a rotating unit, disposed with the first axial direction as the rotating axle and having a first rock arm and a second rock arm, wherein the cam contacts the first rock arm, and one of the driven gears is disposed on the second rock arm, wherein the cover has a propping element while the first rock arm has a first guiding arc, and the propping element props the first rock arm when the cover is closed relative to the frame, and wherein the cam pushes the first rock arm to drive the rotating unit to rotate about the first axial direction with the propping element moving along a profile of the guiding arc, and then an engagement between the driven gear disposed on the second rock arm and another driven gear engaged therewith is released by departing the driven gear disposed on the second rock arm from the driven gear engaged therewith when the cover is opened relative to the frame.