Patent ID: 8511667

Claim:
An automatic document feeder, comprising: a paper pick-up device for transmitting a paper into said automatic document feeder; a first roller assembly located downstream of said paper pick-up device for transmitting said paper, and comprising: a first shaft rotated at a first speed; a first roller sheathed around said first shaft for transmitting said paper; and a power coupling device located at a side of said first roller, wherein said first shaft has a protrusion structure, and said power coupling device has a concave structure, wherein said protrusion structure is accommodated within said concave structure, and wherein said concave structure has a slot; and a second roller assembly located downstream of said first roller assembly for transmitting said paper, and comprising: a second shaft; and a second roller sheathed around said second shaft, and driven to be rotated at a second speed by said second shaft, thereby transmitting said paper, wherein when said power coupling device is connected with said first shaft and said first roller, said first roller is driven to be rotated at a third speed by said first shaft, so that said paper is transmitted to said second roller, wherein said third speed is lower than said second speed, wherein when a front edge of said paper is moved to said second roller and said paper has not been completely departed from said first roller, said first roller is driven to be rotated at said second speed by said paper, so that a power connection between said first roller and said first shaft is released by said power coupling device, wherein after said paper is completely departed from said first roller and while said power connection between said first shaft and first roller is released, said first roller reaches a static status.