2D visual micro-position measurement based on intertwined twin-scale patterns

Position measurement at nanoscale currently raises issues such as making significant compromise between range and resolution or as the difficulty to measure several directions with a single sensor. This paper presents a novel visual method to measure displacements at nanometric scale along two axes. This method allows subpixelic measurement of position by using a pseudo-periodic pattern observed by a regular visual setup. This micrometric pattern corresponds to the intertwining of two perpendicular copies of a single-axis pattern made of two frequency carriers with slightly different periods. It was realized in clean room by photolythography of aluminium on glass. The algorithm is based on a twin scale principle, itself based on direct phase measurement of periodic grids. Experiments are performed at video rate (30 fps) and show a linearity below 0.16% and a repeatability below 14 nm over an unambiguous range of 221 mu m. A resolution below 0.5 nm is demonstrated by the use of 2000 images. The method can be adjusted to different ranges, according to the needs. (C) 2016 Elsevier B.V. All rights reserved.