Periodic error evaluation system for linear encoders using a homodyne laser interferometer with 10 picometer uncertainty

An ultraprecision system to evaluate the periodic error of linear encoders (PEL) has been developed. Our system is based on a homodyne laser interferometer as a reference scale. Conventional studies which used an interferometer with unknown periodic error resulted in insufficient reliability because the periodic error of an interferometer (PEI) directly overlaps on the evaluated PEL. In this study, we explicitly reveal the homodyne interferometer in the proposed system has a sufficiently small PEI of less than 10 pm. This PEI is determined by analyzing the amplitude variation of interference signals, which we refer to as “self-evaluation method.” We have demonstrated the applicability of the proposed system through an actual evaluation of one of the most precise linear encoders with a PEL of sub-nanometer order.