3-D Surface Profilometry for Objects Having Extremely Different Reflectivity Regions

Abstract

A novel surface profilometry method is proposed to overcome a difficult surface measuring problem when encountering a measured surface simultaneously having specular and scattering reflective conditions. Most moire projection scanning methods effectively work on scattering or diffusing reflectivity objects, in which it assumes the object emitted light to be well captured by optical sensors. However, in reality, this assumption does not stand anymore when measuring a surface possessing both scattering and specular conditions. Therefore, to resolve the problem, the proposed method proposes a novel dual optical sensing configuration by employment of two optical sensors with two different viewing angles, in which one captures scattered reflective light and while another detects specular surface light with respect to the surface for achieving simultaneous full-field surface profilometry. The measured deformed fringes from both the sensors can be further transformed to 3-D depth information and merged together for full-field surface reconstruction. Some calibration targets and industrial objects were measured to verify the feasibility and accuracy of the developed method. The experimental result shows that the method can effectively overcome the above-mentioned problem. The measurement repeatability with one standard deviation can be controlled less than 0.3 and 2.0 μm, respectively for specular and scattering surfaces simultaneously. The method provides a significant advance in in-situ automated optical inspection (AOI).