Compensating probe radius in free surface modeling with CMM

In surface measurement system using a touch probe, probe radius compensation is a key to accuracy. In this paper, the authors investigate methods for compensating probe radius so that the surface equation for an unknown free-surface can be efficiently derived. The algorithm developed derives a surface equation by an iterative procedure consisting of: a) estimation, b) verification, and c) modification. As the estimation and verification procedures are based on both geometric modeling and surface measurement, modeling accuracy can be ensured. Further, since modifications are made only for the surface region exceeding the tolerance limit, an accurate surface equation can be obtained with less computation and measurement time. The validity and effectiveness of the algorithm is tested via both numerical simulation and real experiment with CMM. The results indicate that the methods developed can be incorporated in the CMM as an explicit means for modeling and verification of free surfaces