An auto document feeder (ADF) is a paper feeding mechanism for a photocopying machine. The ADF can convey a whole stack of paper sheets one by one to make them pass through a scanner of the photocopying machine for scanning operations. A common photocopying machine can only scan one side of the paper sheet. By adding another scanner in the ADF, the other side of the paper sheet can also be scanned, so both sides of the paper sheet can be scanned in one paper feeding operation.
A simple configuration method, like disclosed in U.S. Pat. No. 7,457,006, U.S. Pat. No. 5,280,368, U.S. Pat. No. 7,411,704 and U.S. Pat. No. 8,730,537, is to include another scanner adjacent to the scanner of the photocopying machine. Generally, the scanner is a contact image sensor (CIS) scanner, so the paper sheet has to be in flat contact with the scanner for precise focus operations and better scanning quality. The two scanners are usually disposed opposite to each other. Therefore, after passing through one scanner, the paper sheet has to turn over instantly to come into flat contact with the other scanner. This motion can be achieved by utilizing a block for pressing paper sheets. However, this tends to cause twisting of the paper sheets and paper jams.
As a result, the target of the inventor is to solve the above-mentioned problems, on the basis of which the present invention is accomplished.