6-DoF Motion Capture With Nanometric Resolutions Over Millimetric Ranges Using a Pseudo-Periodic Encoded Pattern

We propose a method to measure the six degrees of freedom (DoFs) of an object moving in space with nanometric resolutions over millimetric ranges. Similar to conventional motion capture systems, a marker is attached to the object and tracked using an imaging system. However, the proposed method relies on digital holography rather than conventional refractive microscopy and involves two complementary measurement principles, that is, interferometry and phase-based motion estimation, applied simultaneously to the hologram of a micro-structured pattern. Interferometry addresses out-of-plane motions, while phase-based motion estimation addresses complementary in-plane displacements to address the six DoFs. Performance metrics, namely, resolution, linearity, range, and repeatability, are evaluated experimentally. Finally, the proposed measurement method is applied to capture the motion of a precision hexapod to demonstrate its potential for 3-D metrology applications at the nanometer scale.