Pre-correction of projected gratings for surface profile measurement

Cuiru Sun; Hua Lu

doi:10.1117/12.839317

25 August 2009 Pre-correction of projected gratings for surface profile measurement

Cuiru Sun, Hua Lu

Proceedings Volume 7375, ICEM 2008: International Conference on Experimental Mechanics 2008; 73754R (2009) https://doi.org/10.1117/12.839317
Event: International Conference on Experimental Mechanics 2008 and Seventh Asian Conference on Experimental Mechanics, 2008, Nanjing, China

Abstract

This paper discusses errors caused by unequal grating pitch in applying the phase-shifted digital grating projection method for object profile measurement. To address the related issues, a new scheme is proposed to effectively improve the uniformity of the projected grating pitch across the object surface with no additional hardware cost. The improvement is mainly realized via a grating pitch pre-correction algorithm assisted by Digital Speckle/Image Correlation (DSC/DIC). DIC is utilized to accurately determine the surface grating pitch variation when an originally equal-pitched grating pattern is slant projected to the surface. With the actual pitch distribution function determined, a pre-corrected grating with unequal pitch is generated and projected, and the iterative algorithm reaches a constant pitched surface grating. The mapping relationship between the object surface profile (or out-of-plane displacement) and the fringe phase changes is obtained with a real-time subtraction based calibration. A quality guide phase unwrapping method is also adopted in the fringe processing. Finally, a virtual reference phase plane obtained by a 3-point plane fitting algorithm is subtracted to eliminate the carrier phase. The study shows that a simple optical system implemented with the mentioned improvements remarkably increase the accuracy and the efficiency of the measurement.

Citation Download Citation

Cuiru Sun and Hua Lu "Pre-correction of projected gratings for surface profile measurement", Proc. SPIE 7375, ICEM 2008: International Conference on Experimental Mechanics 2008, 73754R (25 August 2009); https://doi.org/10.1117/12.839317

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