Advanced linear encoder calibration system with sub-nanometer resolution

Calibration of linear encoders has conventionally been performed using an optical interferometer for reference. Calibration using the optical interferometer, however, cannot fulfill the accuracy and stability requirements when the linear encoders exhibit sub-nanometer resolution. This study describes a new calibration method developed using the picometer resolution laser holographic scale as a reference, employing a range-dependent and minimum error-variance algorithm. The method has been evaluated via comparison tests with conventional optical-interferometer-based methods. Moreover, it has also been verified to achieve higher resolution, accuracy, and higher stability during the measurements, even in the atmospheric environment.