Patent ID: 8497469

Claim:
A rotary encoder comprising: a scale including a first pattern and a second pattern different from the first pattern and configured to be rotatable around a rotation axis; a light source configured to illuminate a light onto the scale; a first detector configured to detect a light transmitted through or reflected on the first pattern to output a first detection signal; a second detector configured to detect a light transmitted through or reflected on the second pattern to output a second detection signal; and a controller configured to generate an eccentricity correction signal based on the first detection signal to correct the second detection signal based on the eccentricity correction signal, wherein one of the first pattern and the second pattern is a spiral pattern that is spirally formed around the rotation axis to detect a rotational angular displacement larger than a predetermined value, and wherein the other one of the first pattern and the second pattern is a radial pattern that is radially formed around the rotation axis to detect a rotational angular displacement smaller than the rotational angular displacement detected by the spiral pattern.