Automatic document feeder

An automatic document feeder, comprising:

• a paper transmitting path including an input tray, an input path, a scanning area, an output path and an output tray in sequence from an upstream to a downstream along a document transmission direction of the automatic document feeder, wherein the upstream is designated at a document entrance and the downstream is designated at a document exit;
• a driving motor for providing driving torque in different directions;
• at least one scan roller and one transmitting roller disposed among the paper transmitting path;
• a pickup device disposed at the upstream of the paper transmitting path to pick documents up under the control of the driving torque;
• an output device including movable pressure rollers and acting rollers which are disposed at the downstream of the paper transmitting path to transmit the documents forward or backward under the control of the driving torque;
• a first driving gear driven by the driving motor and disposed between the pickup device and the output device;
• a transmitting gear swing arm axially hinged with the first driving gear and equipped with a transmitting gear set, the transmitting gear swing arm being swingable according to the driving torque in the different directions between a first position meshing the transmitting gear set with the pickup device and a second position idling the transmitting gear set;
• an actuator connected with the output device for controlling the movement of the pressure rollers;
• and
• a braking device disposed on the output device which locks the transmitting gear swing arm according to the position of the output device,
• wherein the transmitting gear set includes a first transmitting gear and a first torque limiter, the first transmitting gear is hinged on the transmitting gear swing arm by means of the first torque limiter and meshed with the first driving gear.