New calibration procedure for measuring shape on specular surfaces

The methodology of phase encoded reflection measurements has become a valueable tool for the industrial inspection of components with glossy surfaces. The measuring principle provides outstanding sensitivity for tiny variations of surface curvature so that sub-micron waviness and flaws are reliably detected. Quantitative curvature measurements can be obtained from a simple approach if the object is almost flat. 3D-objects with a high aspect ratio require more effort to determine both coordinates and normal direction of a surface point unambiguously. Stereoscopic solutions have been reported using more than one camera for a certain surface area. This paper will describe an alternative approach that is well suited for the implementation in industrial testing stations. The mathematical background and the algorithms will be explained and application samples are shown to demonstrate the performance in practical use.