Robust positioning for measurement of freeform surfaces

Form characterization of a manufactured freeform surface can be conducted by aligning the sampling points on a manufactured surface and comparing that with the design geometry through the localization. In this paper, a robust localization method named fiducial aided positioning method (FAPM) is developed to evaluate freeform surfaces with high efficiency and precision. The FAPM method makes use of fiducials to form a Fiducial-aided Computer Aided Design (FA-CAD) of the freeform surface which not only establishes an inherent surface feature but also links the different coordinate systems among design coordinate frame, machine tool and the measurement instrument. To verify the capability of the proposed method, a series of experiments have been undertaken. As compared with the traditional freeform measurement method such as least squared method, it is interesting to note that the robustness and accuracy of the measurement is significantly enhanced by the FAPM.