Retard roll with integral torque limiting slip clutch with reversing bias

摘要

A retard sheet feeder that utilizes a slip clutch with an integral biasing device to separate double fed sheets. A retard roll is provided in circumferential contact with a feed roll to form a drive nip. The retard roll is free to rotate in the feeding direction by the use of a spring that is axially aligned with the roll and allows the roll to slip in the feed direction once a predetermined torque level is reached. The spring may be either internal to the roll or external to the roll. When the drive torque to the retard roll is reduced such as when a double sheet is in the drive nip, the torque is not sufficient to overcome the stored spring energy and the roll is rotated in a reverse direction by the spring to drive the double sheet out of the nip. Once the double sheet is removed from the nip the frictional contact between the drive roll, a single sheet and the retard roll again winds the spring to the predetermined torque level at which point the spring slips allowing the retard roll to overrun in the feed direction.