6. A control method for a document feeding device, the document feeding device including: a carrying unit capable of carrying thereon a plurality of documents; a drawing device to draw and supply the carried documents; a drawing device drive source to drive the drawing device; a separation unit including a separation device to separate the supplied documents one by one; a separation device drive source independent of the drawing device drive source and to drive the separation device; a conveying device to convey the separated documents; a reading unit including a reading device to read information of the conveyed documents; a discharge device to discharge the read documents; a first document detector provided between a document set position of the carrying unit and the separation unit to detect the documents; a second document detector provided downstream of the separation unit and near a separation position of the separation unit to detect the documents; and a controller to control operation of the drawing device based on detection results obtained by the first document detector and the second document detector, the control method comprising: detecting a trailing end of each of the documents in sheet feeding of the documents using the first document detector and the second document detector; predicting the timing at which the trailing end of each of second and subsequent documents passes the first document detector; and lowering a pickup roller of the drawing device based on the length of a first document wherein the control of the operation of the drawing device is a pickup synchronization control, and wherein the pickup synchronization control is not performed when a mixed mode is set to read documents of different document lengths.
6. A control method for a document feeding device, the document feeding device including: a carrying unit capable of carrying thereon a plurality of documents; a drawing device to draw and supply the carried documents; a drawing device drive source to drive the drawing device; a separation unit including a separation device to separate the supplied documents one by one; a separation device drive source independent of the drawing device drive source and to drive the separation device; a conveying device to convey the separated documents; a reading unit including a reading device to read information of the conveyed documents; a discharge device to discharge the read documents; a first document detector provided between a document set position of the carrying unit and the separation unit to detect the documents; a second document detector provided downstream of the separation unit and near a separation position of the separation unit to detect the documents; and a controller to control operation of the drawing device based on detection results obtained by the first document detector and the second document detector, the control method comprising: detecting a trailing end of each of the documents in sheet feeding of the documents using the first document detector and the second document detector; predicting the timing at which the trailing end of each of second and subsequent documents passes the first document detector; and lowering a pickup roller of the drawing device based on the length of a first document wherein the control of the operation of the drawing device is a pickup synchronization control, and wherein the pickup synchronization control is not performed when a mixed mode is set to read documents of different document lengths. 7. The control method according to claim 6 , wherein the control of the operation of the drawing device is a high-speed conveyance control which sets the document conveying speed of the drawing device to be higher than the document conveying speed of the separation device.