Patent ID: 8289591

Claim:
A sheet-fed image scanning method adapting a contact image sensor (CIS) as a scanning element, wherein the scanning method comprises: equipping the CIS scanning element with at least two sheet-feeding rollers connected with a driven roller for enabling a to-be-scanned sheet to be fed into/out between the sheet-feeding rollers and the driven roller; the driven roller performing elastical ascending/descending according to the thickness of the to-be-scanned sheet when the to-be-scanned sheet is fed in, wherein the CIS scanning element performs constant distance scanning with respect to the to-be-scanned sheet; wherein the scanning method further comprises the ascending/descending of the driven roller comprises a first-level floating program, and when the to-be-scanned sheet has a first thickness, the driven rollers perform a first-level floating equivalent to the first thickness so that during scanning process, the to-be-scanned sheet and the CIS scanning element conform to the scanning condition of the range of optimum scanning focal distance; wherein the ascending/descending of the driven rollers comprises a second-level floating program, the shift of the second-level floating is larger than the shift of the first-level floating, and in the to-be-scanned sheet having a second thickness larger than a predetermined value, the driven rollers first is floated to a predetermined value and then perform a second-level floating together with the CIS scanning element, wherein the distance of the second-level floating is the difference between the second thickness and the predetermined value, so that the distance between the scanning surface of the to-be-scanned sheet and the CIS scanning module conforms to the scanning condition of the range of optimum scanning focal distance.