Torque limiting roller and medium separating mechanism using the same

A medium separating mechanism, comprising:

• a feeding roller for providing driving torque;
• and
• a torque limiting roller driven by the driving torque of the feeding roller, the torque limiting roller comprising:
• a shaft comprising a first end and a second end;
• a frictional unit mounted on the first end of the shaft;
• a roller assembly rotatably mounted on the shaft and comprising a first end and a second end, wherein the first end of the roller assembly is in frictional contact with the frictional unit;
• a fixing unit mounted on the second end of the shaft;
• and
• an elastic unit mounted on the shaft, disposed between the fixing unit and the roller assembly, and contacting with the second end of the roller assembly and the fixing unit to provide a normal force between the frictional unit and the roller assembly and thus to provide limiting torque, wherein:
• a direction of the limiting torque is the same as a rotating direction of the driving torque, and a value of the limiting torque is smaller than a value of the driving torque so that media between the feeding roller and the torque limiting roller are separated to allow one of the media contacting with the feeding roller to be transported past the feeding roller and the torque limiting roller.