US Patent 7327502 Sheet-fed scanning device capable of detecting a document edge

A sheet-fed scanning device capable of detecting a document edge includes a scanning module and an automatic document feeder. The scanning module scans a document with a light ray. The automatic document feeder feeds the document across a scanning region on a sheet passageway for the scanning module to scan. In this invention, a section of a guide plate of the sheet passageway located within the scanning region is formed with a concave portion, wherein the document moving across the scanning region is located between the concave portion and the scanning module, such that the intensity of a first brightness of the concave portion sensed by the scanning module is far smaller than the intensity of a second brightness of the document sensed by the scanning module. Thus, it is possible to facilitate the document edge detection and the document skew correction.