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 μm. 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.