Abstract The dual-frequency grating measurement theory is proposed in order to carry out the measurement of a discontinuous object. Firstly, the reason why frequency spectra are produced by low frequency gratings and high frequency gratings in the field of frequency is analysed, and the relationship between the wrapped-phase and the unwrapping-phase is discussed. Secondly, a method to combine the advantages of the two kinds of gratings is proposed: one stripe is produced in the mutation part of the object measured by a suitable low frequency grating designed by MATLAB, then the phase produced by the low frequency grating need not be unfolded. The integer series of stripes is produced by a high frequency grating designed by MATLAB based on the frequency ratio of the two kinds of gratings and the high frequency wrapped-phase, and the high frequency unwrapping-phase is then obtained. In order to verify the correctness of the theoretical analysis, a steep discontinuous object of 600×600 pixels and 10.00 mm in height is simulated and a discontinuous object of ladder shape which is 32.00 mm in height is used in experiment. Both the simulation and the experiment can restore the discontinuous object height accurately by using the dual-frequency grating measurement theory.
Received: 14 February 2009
Revised: 08 April 2009
Accepted manuscript online:
Fund: Project supported by the
Science-Technology Program Research Foundation of Hunan Province,
China (Grant No 2009FJ3187) and the 11\rm th Five-year Plan for
Key Construction Academic Subject (Optics) of Hunan Province, China
(Grant No 06GXCD02).
Cite this article:
Qiao Nao-Sheng(乔闹生),Cai Xin-Hua(蔡新华), and Yao Chun-Mei(姚春梅) Measurement of a discontinuous object based on a dual-frequency grating 2009 Chin. Phys. B 18 4881
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