Document feeding devices for image reading apparatus

摘要

A helical gear connected to a lower discharge roller is made movable in its axial direction toward a bracket when a stepping motor is activated. A friction pad formed from felt or sponge rubber, for example, is attached to a side surface of the helical gear that is located face to face with the bracket. When the stepping motor is energized, the helical gear shifts toward the friction pad and the side surface of the helical gear comes in sliding contact with the friction pad. Resultant frictional resistance produces a braking force which acts on the rotating lower discharge roller. An overrun of the lower discharge roller due to a backlash between engaging gears is prevented even when an upper transfer roller exerts a forward-pushing force on a rear end of a sheet of an original document.