Acer S2W 3300U Service Manual - Page 19

B. Pulley and Driving Belt This device translates rotation motion into linear motion. Two pulleys support the driving belt, and it transmits linear motion when the pulleys rotate. Part of the driving belt is fixed in the carriage, so that the optics mechanism can have a linear motion. The belt tension is a critical factor in the scanning process. A proper belt tension is decisive for a perfect transmission. The belt tension is adjusted by the spring fixed on the pully.