Patent ID: 7658374

Claim:
A sheet feeder in which a pick roller picks a sheet stacked in a hopper and transports the sheet toward a separating section at which a separator roller and a brake roller are provided, and the separator roller and the brake roller transport the sheet one by one, the sheet feeder comprising: a first unit, provided on the brake roller, and to detect a rotational speed of the brake roller; a second unit, provided in the separating section, to detect a speed of the sheet; a third unit, provided on the separator roller, to detect a rotational speed of the separator roller, and a controller, to determine an entry state and to calculate a slip ratio of the sheet with respect to the separator roller based on: the speed of the sheet in the separating section, the rotational speed of the separator roller, and the rotational speed of the brake roller, and to optimally control a force acting in separation for the sheet according to the entry state and the calculated slip ratio.