Multi-degree-of-freedom displacement measurement system for milli-structures

A new multi-degree-of-freedom measurement system for milli-structures is presented. This methodology is based on optical beam deflection method and triangulation. It employs a diffraction grating as a reflective object, which reflects an incident laser beam into several directions. To obtain the pose information of a measured object, the detecting positions of zeroth- and first-order diffracted rays are measured using three two-dimensional detectors. From these values, we can calculate six-degree-of-freedom displacement through a kinematic analysis. The performance was evaluated with resolution, measurement errors and crosstalk. The results show that measurement errors and maximum crosstalk are within ±0.5 µm in translation and ±2'' in rotation. As an application, we measured the multi-DOF motion of a bimorph type PZT actuator and obtained its frequency response function.