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

• Published in: Sensors and actuators. A. Physical. Vol. 248; pp. 272 - 280
• Main Authors: Guelpa, Valérian, Sandoz, Patrick, Vergara, Miguel Asmad, Clévy, Cédric, Le Fort-Piat, Nadine, Laurent, Guillaume J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2016; Elsevier
• Subjects: Automatic; Computer Science; Data Structures and Algorithms; Direct phase computation; Displacement sensing; Engineering Sciences; Mechanics; Nanometric precision; Physics; Subpixelic; Two-axes pattern; Displacement sensing; Two-axes pattern; Subpixelic; Nanometric precision; Direct phase computation
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2016.08.002

•A new pattern design for micro-positioning along two directions is proposed.•The accuracy of the method is due to the phase-measurement of a periodic pattern.•The range is improved due to the twin-scale principle of the pattern.•Real-time experiments show nanometric performances over an unambiguous large range.•The method could be extended to others scales. 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 (30fps) and show a linearity below 0.16% and a repeatability below 14nm over an unambiguous range of 221μm. A resolution below 0.5nm is demonstrated by the use of 2000 images. The method can be adjusted to different ranges, according to the needs.