An absolute angle recovery method for dual-interferometer-based rotational stages

A new absolute angle recovery method for dual-interferometer-based rotational stages is presented. The high resolution of laser interferometers makes this sensor particularly suitable for high-precision rotational stages (comprising two parallel interferometer heads separated by a fixed distance). However the incremental operation of the sensor results in relative angle reference. The proposed method establishes an absolute angle reference system based on the characteristic movement of the rotational stage throughout the full angular range. The method is successfully applied in a high-precision rotational stage and its performance is evaluated with an external dual-interferometer system showing an accuracy of ±1.65μrad (3σ).