A high subdivision and light fluctuation-insensitive approach for grating displacement sensors

This paper presents an innovative GPI-NCCSR subdivision approach for grating displacement sensor based on grating projection imaging (GPI) and normalized cross-correlation sub-pixel registration (NCCSR) algorithm, achieving high subdivision within the grating pitch and exhibiting robust immunity to fluctuations in light source intensity. The GPI method facilitates the creation of long-period longitudinal moiré fringes more readily, and capturing moiré fringe information with a line-scan CCD allows for an extremely high subdivision. The NCCSR approach to displacement detection is impervious to signal amplitude fluctuations, thus enhancing the stability of the subdivision. Moreover, the sub-pixel registration algorithm can improve resolution even further. The experiments demonstrate that the proposed subdivision method achieves a displacement resolution superior to 4nm_RMS, indicating a subdivision multiple within the 20µm pitch exceeding 5000 while remaining unaffected by variations in light intensity. Besides, the sensor exhibits repeatability accuracy better than 0.05% across various measurement points, with a linearity of 0.17% within a 3mm range.