Measurement of a discontinuous object based on a dual-frequency grating

The dual-frequency grating measurement theory isproposed in order to carry out the measurement of a discontinuousobject. Firstly, the reason why frequency spectra are produced bylow frequency gratings and high frequency gratings in the field offrequency is analysed, and the relationship between the wrapped-phase andthe unwrapping-phase is discussed. Secondly, a method to combine theadvantages of the two kinds of gratings is proposed: one stripe isproduced in the mutation part of the object measured by a suitablelow frequency grating designed by MATLAB, then the phase produced bythe low frequency grating need not be unfolded. The integer series ofstripes is produced by a high frequency grating designed by MATLABbased on the frequency ratio of the two kinds of gratings and thehigh frequency wrapped-phase, and the high frequency unwrapping-phaseis then obtained. In order to verify the correctness of thetheoretical analysis, a steep discontinuous object of 600×600pixels and 10.00~mm in height is simulated and a discontinuous objectof ladder shape which is 32.00~mm in height is used in experiment.Both the simulation and the experiment can restore the discontinuousobject height accurately by using the dual-frequency grating measurement theory.