Based on the projection moiré method and heterodyne interferometry, this study proposes an alternative method for reconstructing the surface profile of an object. Obliquely illuminating a linear grating with an expanding collimated light, a self-image of this grating can be generated and projected on the surface of the tested object. The grating fringes distorted by the surface profile are imaged on the reference grating to form the moiré fringes. These moiré fringes are then captured by a CMOS camera. If the projection grating moves with a constant velocity along the grating plane, each pixel of the CMOS camera records a series of sampling points of the sinusoidal wave. These sinusoidal waves behave like heterodyne interferometric signals. Hence, the accurate and stable phase distribution of the tested object surface can be obtained using the IEEE 1241 least-squares sine fitting algorithm and 2D phase unwrapping. Substituting the phase values into the derived equation, the surface profile of the tested object can be reconstructed. The experiments in this study verified the feasibility of this method, showing a measurement resolution of approximately 1.9 μm. The proposed measurement method has the merits of both the projection moiré method and the heterodyne interferometry.
- Heterodyne interferometry
- Surface profile measurement