Patent ID: 7654517

Claim:
An image scanning apparatus comprising: a document tray arranged to receive a plurality of documents; an image scanning unit arranged to scan the documents; a transfer unit arranged to transfer the documents on the document tray one by one toward the image scanning unit; a lifting and lowering device arranged to lift and lower the document tray; a height detection sensor arranged to detect an upper surface height of the documents stacked on the document tray; and a control unit arranged to control the lifting and lowering device; wherein the height detection sensor detects that the upper surface height is lower than a predetermined height due to the transfer of the document by the transfer unit such that: in a first case of a relatively low document scanning speed, the control unit elevates the document tray to a target height which is higher by a predetermined distance from a height during an inter-transfer time between completion of the document transfer and start of a subsequent document transfer, the height being that at which the height detection sensor detects that the upper surface height is not lower than the predetermined height; in a second case of a relatively intermediate document scanning speed that is faster than the low document scanning speed, the control unit elevates the document tray at predetermined pitches in each transfer of one document during the inter-transfer time until the upper surface height reaches the target height; and in a third case of a relatively fast document scanning speed that is faster than the intermediate document scanning speed, the control unit tentatively interrupts the transfer of the document by the transfer unit to elevate the document tray until the upper surface height reaches the target height, and then the control unit resumes the transfer of the document by the transfer unit.