A three-step displacement measurement method for a 3-DOF macro-micro positioning stage

A high-performance displacement measurement method for the displacement measurement of a three degree of freedom (3-DOF) macro-micro positioning stage based on the micro-vision measurement system is proposed. The method is built up by three steps. In the first step, a fast search algorithm combined with triangular relations and a ring projection with illumination and noise correction is adopted to achieve the selection of candidate pixels. Subsequently, an orientation code based algorithm is adopted to determine the integer-pixel displacement and rotation angle estimation. The third step is to obtain the sub-pixel displacement through a similarity function based algorithm. Simulations are carried out, and the results show that the proposed method has the characteristics of translation and rotation invariance, and the matching accuracy can reach 0.01-pixel theoretically. Moreover, the proposed method consumes less time than that of the orientation code and pseudo-Zernike moment based algorithm. Finally, a capacitance sensor measurement system is established to compare the accuracy of the proposed method. The experiment results demonstrate that it has a high accuracy.