Patent ID: 8454008

Claim:
A retard roller of an automatic document feeder for providing a frictional force to separate a first document and a second document from each other, said first document lying on said second document, said retard roller being disposed in a feeder cover of said automatic document feeder, said feeder cover comprising a retard roller receptacle and a receiving structure beside said retard roller receptacle, said retard roller comprising: a rotating shaft disposed within said retard roller receptacle and rotatable with respect to said feeder cover; a switching wheel disposed beside said rotating shaft, connected to said rotating shaft, and synchronously rotated with said rotating shaft, wherein said switching wheel has a first locking region and a second locking region; a stopping rod disposed within said receiving structure, and comprising a confining part, wherein said confining part is inserted into said first locking region or said second locking region of said switching wheel, and said confining part is blocked by a blocking part, so that said stopping rod is hindered from rotating in a first rotating direction; a retard sleeve member sheathed around said rotating shaft, and having a first contact surface exposed outside said retard roller receptacle, and plural soft elements disposed on said rotating shaft and contacted with said retard sleeve member for increasing a contact area between said second document and said retard sleeve member, wherein each of said soft elements has a rectangular shape, and wherein said rotating shaft further comprises plural grooves for receiving corresponding soft elements; wherein when said first document and said second document are transported into said automatic document feeder, said retard sleeve member is contacted with said second document to generate said frictional force, wherein when said second document is moved in a sheet-feeding direction, said stopping rod is blocked by said blocking part to hinder said rotating shaft from rotating in said first rotating direction, so that said first contact surface is still exposed outside said retard roller receptacle, wherein when said rotating shaft is rotated in a second rotating direction reverse to said first rotating direction, said stopping rod is rotated in said second rotating direction in response to rotation of said rotating shaft, and said confining part is moved from said first locking region to said second locking region, so that a second contact surface is exposed outside said retard roller receptacle.