Adaptive projection moiré method for arbitrarily arranged light path system.

In the projection moiré method, the projected fringe with a constant period usually generates a moiré pattern with nonuniform fringe spacing, which increases the low modulation regions and local measurement error. In this work, an adaptive moiré pattern generation method for the projection moiré system is developed. By formulating the relationship between the surface contour and moiré fringe spacing, the period of the projected fringe is modulated to acquire a uniform moiré pattern and highly improve the full-field measurement precision. The corresponding calculation algorithm is developed to obtain the 3D morphology. The proposed method is applicable to an arbitrarily arranged projection moiré system on any continuous surface without the phase jump error. A series of experiments are carried out, and the results are discussed in detail.

Novel method for increasing accuracy of projection moiré contouring of large surfaces.

Projection moiré is a high resolution, non-contact, full field method for measuring out-of-plane displacements. Here, we develop a novel model for projection moiré system and derive a universal formula expressing the relation between phase variation and out-of-plane displacement. In order to eliminate the error caused by mismatching of pixels and changing of sensitivity coefficient, an iterative algorithm is presented which expands measurements to the magnitude of depth of field. Computer simulations and actual experiments prove the validity of the proposed method.

Three-dimensional shape measurement with an arbitrarily arranged projection moiré system.

A complete description of a three-dimensional shape measurement method with an arbitrarily arranged projection moiré system is presented, including the mathematical derivation of theoretical equations, phase-to-height calibration technique, and experimental result of practical object. The proposed method requires neither a specific system setup configuration nor a manual determination of system geometric parameters, and it yields high measurement resolution and accuracy while allowing the system components to be arbitrarily positioned. A real experiment has been conducted to verify the validity of this method.

Phase extraction algorithm considering high-order harmonics in fringe image processing.

A phase calculation method using discrete Fourier series (DFS) is proposed to eliminate the effects of nonsinusoidal characteristics. In this method, the fundamental coefficients are extracted from continuous N samples in one cycle by DFS, with which four images with π/2 intervals are reconstructed, and then more accurate phase distribution can be further obtained. This method is applicable for improving the precision of the traditional phase-shifting algorithm. Its effectiveness and accuracy are verified by computer simulations and moiré fringe and projecting fringe experiments with about 85% of the phase error reduced compared with a four-step phase-shifting algorithm, about 70% reduction compared with a 16-step phase-shifting algorithm.