17 June 2009 Novel instrumentation for interferometric nanoscale comparator
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Displacement sensors with nanometer resolution used in precision engineering demand precise scale calibrations. Presented paper deals with the description of subsystems of a novel interferometric nanocomparator. High speed digital quadrature detector based on digital signal controller is used here for processing of the X-Y signals from the detection unit of the interferometer. Digital filtering increases signal to noise ratio and allows achievement of sub-nanometer resolution and accuracy of the laser interferometer. The refractive index of the air is computed continuously from the current atmospheric values using Edlen's formula. High dynamic range of the mirror displacement setting is achieved using a two stage positioning system formed of a linear guide way and piezoelectric actuators. The linear guide way is used for open-loop coarse positioning with 50 nm accuracy and up to 100 mm of displacement. Piezoelectric actuators in servo-loop linked to the interferometer value are used for fine positioning with better than 1 nm accuracy over a 5 μm range. Due to imperfections of the linear guide way with ball carrier bearings, random deviations of the mirror from the ideally perpendicular position to the laser beam may introduce uncertainties to the measurement. To compensate this, the position of the beam reflected from the mirror is measured by a 4-quadrant light detector. Using the piezoelectric actuators in servo-loop mode the control part of the system actively stabilizes the mirror in a position perpendicular to the laser beam.
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Martin Cizek, Martin Cizek, Zdenek Buchta, Zdenek Buchta, Bretislav Mikel, Bretislav Mikel, Josef Lazar, Josef Lazar, Ondrej Cip, Ondrej Cip, } "Novel instrumentation for interferometric nanoscale comparator", Proc. SPIE 7389, Optical Measurement Systems for Industrial Inspection VI, 73892Y (17 June 2009); doi: 10.1117/12.827515; https://doi.org/10.1117/12.827515

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