Patent ID: 8066274

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 comprising: a first sleeve having a sleeve inner tube; a second sleeve accommodated within said first sleeve, and having a sleeve outer tube, wherein said sleeve outer tube is arranged at an end of said second sleeve and contacted with an end of said sleeve inner tube; a separation pad sheathed around said first sleeve, and contacted with said second document; a helical spring accommodated within said first sleeve, a first end of said helical spring is sheathed around said sleeve outer tube to define a first spring segment, a second end of the helical spring is sheathed around said sleeve inner tube to define a second spring segment, said first spring segment has a first spring inner diameter, and said second spring segment has a second spring inner diameter smaller than said first spring inner diameter; a one-way clutch accommodated within said second sleeve for preventing said second sleeve from rotating in a first rotating direction; and a rotating shaft penetrated through said first sleeve, said second sleeve and said one-way clutch, wherein when said second document is moved in a first direction, said first sleeve is rotated in said first rotating direction, and said second sleeve fails to be rotated in response to said one-way clutch, so that said first spring segment is fixed on said sleeve outer tube and said second spring segment is twisted with respect to said sleeve inner tube to generate a first damping torque, wherein when said second document is moved in a second direction opposed to said first direction, said first sleeve is rotated in a second rotating direction, said first spring segment is fixed on said sleeve outer tube, and said second spring segment is fixed on said sleeve inner tube, so that said second sleeve is rotated with said first sleeve and said one-way clutch is rotated with respect to said rotating shaft to generate a second damping torque, wherein said first damping torque is greater than said second damping torque.