CAD-Model Based Inspection of Sculptured Surfaces

Increasing demands on high precision manufacturing of parts with complex surfaces have been observed in the last several years. Although significant progress has been made in precision machining of complex surfaces, precision inspection of such surfaces remains a difficult problem. A critical issue in surface inspection is localization of design coordinate system (DCS) on a measurement machine. As localization has to rely on manufactured surface features that contain imperfections, a matching method is essential in order to achieve an accurate location. This paper presents a CAD-model based inspection approach to precision inspection of sculptured surfaces. The link between an inspection module and a CAD system was established through neutral files in Pro/Engineer. Surfaces are represented in bicubic parametric spline models. An effective pseudoinverse algorithm was developed and implemented for localization. It consists of two iterative operations: 1), constructing a pseudo transformation matrix, and 2), point matching. Since this approach does not involve solving nonlinear equations for the parameters of positions and orientations, it is fast and robust. The algorithm was implemented and tested with several examples. It is effective and can be used in industry for sculptured surface inspection.