using " optical encoder " as keyword to search relatated material! W% p5 o, b& @; q1 m7 Y
ex: * j5 E4 f* X; D4 U( B$ X ^BEI 5 C! ]9 e6 t3 A: P$ u9 ?http://www.motion-control-info.com/encoder_glossary.html & K" p# w' L( W/ c2 L Y9 l E0 ^+ I; p t. y$ G( u" }
good luck