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A self-calibration algorithm is described that allows testing the out-of-plane error motion of two-dimensional profiling stages by using a flat artifact whose accuracy is unknown. The algorithm suppresses artifact-related calibration errors in consideration of the geometrical congruence of three separate profile measurements taken with different orientations of a single artifact. Usefulness of the self-calibration algorithm is verified through computer simulation as well as actual experimental testing. Test results show that the calibration accuracy is free from artifact imperfection and only minimally affected by random measurement errors encountered during the process of calibration. [Copyright &y& Elsevier]

A new method of thermal stabilization that uses gallium as an isothermal heat exchanger is presented. Gallium maintains a fixed temperature near 29 °C when it melts, and the resultant temperature sustains extremely good stability against ambient change of temperature and pressure. This thermo-physical property allows gallium to be utilized as an isothermal medium that is capable of performing precise thermal stabilization at near room temperature without intensive care on temperature sensing and heat control. In this investigation, an isothermal gallium chamber is designed and an ultraprecision level of temperature stabilization to ±1 mK is demonstrated with the aid of Fabry–Perot interferometry. [Copyright &y& Elsevier]

Abstract: This paper describes a three-probe system that can be used to measure the parallelism and straightness of a pair of rails simultaneously. The parallelism is measured using a modified reversal method, while the straightness is measured using a sequential two-point method. The measurement algorithms were analyzed numerically using a pair of functionally defined rails to validate the three-probe system. Tests were also performed on a pair of straightedge rails with a length of 250mm and a maximum straightness deviation of 0.05μm, as certified by the supplier. The experimental results demonstrated that the parallelism measurement algorithm had a cancellation effect on the probe stage motion error. They also confirmed that the proposed system could measure the slope of a pair of rails with an accuracy of about 0.06μrad. Therefore, by combining this technique with a sequential differential method to measure the straightness of the rails simultaneously, the surface profiles can be determined accurately and the stage error eliminated. The measured straightness deviation of each straightedge was less than 0.05μm, consistent with the certified value. [Copyright &y& Elsevier]

Abstract: A new metrological method is presented that performs simultaneous real-time measurements and compensates for 5-DOF parasitic motion errors in translation stages for precision profiling of optical surfaces. Two plane mirrors are used to obtain motion-dependent interferometric fringes generated by the optical principles of Twyman–Green interferometry. The fringes generated are monitored using high-speed 2D photodiode arrays and analyzed to determine the five separate motion error components in real time. Simultaneously, null control is performed to suppress the measured motion errors independently using piezoelectric actuators through real-time feedback control while the machine axis is moving. The experimental results demonstrate that 5-DOF parasitic motion errors are effectively measured and compensated to within 10nm for translational motions and 0.15arcsec for angular motions. [Copyright &y& Elsevier]

Abstract: This paper describes an estimation and correction method for the two-dimensional (2D) position errors of a planar XY stage that is driven along the Y-axis by two linear motors. The 2D position errors of the stage were estimated and corrected based on measured motion errors from a conventional laser interferometer system. To compensate for the planar XY stage 2D position errors, corrections were introduced for the yaw, perpendicular, straightness and 1D position errors along each axis, which are predominantly caused by linear scale, yaw, and pitching motion errors. The effect of the motion error corrections was evaluated by diagonal measurements based on the ISO230-6 standard and six different 1D position error measurements along the X and Y-axes. By applying error motion corrections, the diagonal systematic deviation at the center point was improved from 499.7μm to 1.16μm, and the estimated maximum 2D position errors were improved to −0.263 and 0.530μm in the X and Y directions, respectively. The diagonal systematic deviation at a corner point was 1.23μm and the estimated maximum difference between the corner and center points improved from −2.603 and 2.603μm to −0.05 and 0.12μm in the X and Y directions respectively. [Copyright &y& Elsevier]