Patent ID: 8182065

Claim:
A motion control system, comprising: a movable component; an optical encoder for detecting a position along an encoder strip based on plural encoder markings, wherein the encoder strip is formed of a second material and the optical encoder is fixedly attached to the movable component; and a first sensor and a second sensor for detecting an index mark on the encoder strip, wherein the index mark is different from the encoder markings and the first sensor and second sensor are spaced apart a fixed distance and mounted to a substrate formed of a first material having substantially no hydroscopic expansion and a linear coefficient of thermal expansion of at least ten times less than a thermal coefficient of expansion of the second material, the substrate fixedly attached to the movable component; wherein the encoder strip having encoder marks on a first portion and the one index mark on a second portion, the encoder strip positioned such that when the movable component is moved along the encoder strip the encoder marks may be detected by the optical encoder, and the at least one index mark is moved sequentially past the first sensor and the second sensor; the first material and the second material having different coefficients of thermal expansion.