Scanner

A scanner, comprising:

• a paper feeding roller set;
• a paper exporting roller set;
• a scanning module, disposed between the paper feeding roller set and the paper exporting roller set;
• a background and calibration roller, disposed side by side next to the scanning module, and the background and calibration roller having a first end and a second end opposite to each other, and comprising a black background section, a white background section and at least one calibration section located between the first end and the second end;
• a main driving assembly, comprising a main power source and a transmission set linked to the main power source, wherein the paper feeding roller set and the paper exporting roller set are linked to the transmission set;
• a first sleeve, sleeving the first end of the background and calibration roller, and linked to the transmission set;
• a torque limiter, disposed between the first end of the background and calibration roller and the first sleeve and contacting the first end and the first sleeve, wherein a torque of the first sleeve is adapted to be transmitted to the background and calibration roller through the torque limiter;
• and
• a stop-driving assembly, selectively abutting against two portions of the background and calibration roller, so as to make the black background section or the white background section of the background and calibration roller facing towards the scanning module.