Dear　editor,
Optical　encoder　is　a　kind　of　angle　sensor,　which　has　been　applied　in　a　variety　of　domains　such　as　astronomy,　vehicles　and　industrial　production.However,　there　always　exist　errors　between　the　measured　angles　and　the　real　angles,　reducing　the　performance　and　safety　of　systems.These　measurement　errors　may　raise　from　various　sources,　like　error　of　installation　and　mechanical　wear.The　sensor　errors　can　be　classified　into　two　categories:random　errors　which　are　difficult　to　completely　eliminate　and　repeatable　errors　(systematic　errors)　which　can　be　effectively　reduced　by　the　compensation　techniques.