Patent ID: 6970272

Claim:
A duplex automatic document feeder comprising: a document stacking tray for stacking a set of documents; a document separating/feeding unit having a document feeding port for separating the set of documents and feeding the documents one by one from the uppermost document thereof; an image reading unit for reading the image data on the first side of the document passing the image reading position; a document inverting unit for inverting the document feeding direction to read the image data on the second side of the document which passes the image reading position after the reading of the first side has been completed; a document discharging unit for piling up the documents on the document-discharging tray after the front and the reverse side of the document of which both-sides have been read is reversed, with the document not passing on the image reading position; a first transporting path for guiding the document from the document separating/feeding unit to the image reading position and having a document set sensor near the document feeding port in the first transporting path; a second transporting path for guiding the document from the said image reading position to the document inverting unit; a third transporting path for guiding the document from the said document inverting unit to a first intersecting point of the first transporting path and from this first intersecting point to the said image reading positing, wherein a first position detecting sensor is located near the first intersecting point; a fourth transporting path for guiding the document from a second intersecting point in the midst of the said third transporting path to the said document discharging unit, wherein a second position detecting sensor is located near the second intersecting point; and a switching member employed in the said second intersecting point which switches the document feeding path from the said document inverting unit to the third transporting path or the fourth transporting path from this intersecting point.