Simultaneous multiple degrees of freedom (DoF) measurement system

This paper presents a newly developed highly accurate interferometric 6 degrees of freedom (DoF) measurement system with Angstrom resolution for displacement and mu rad resolution for angle measurement, respectively. The new interferometer is based on a modified homodyne Twyman-Green interferometer concept. It uses a novel signal acquisition and processing approach whereby a spatial interferogram is captured by a CMOS camera and the registered fringe pattern is transformed into its frequency spectrum [1]. The spectral representation of a movement of e.g. a positioning stage is analyzed for its major components: the phase information directly correlates with the displacement of the stage, while a possible rotational motion causes a shift in the frequency spectrum. The developed compact 6 DoF head uses multiple rays in parallel to detect x-y-z displacements and roll-pitch-yaw movements.