For different tasks, probe tip should be changed in the 3D vision coordinate measuring system and the accurate determination of probe tip center position is critical. A novel and simple approach for calibrating the probe tip center position of the light pen is presented in this paper. Hundreds of images of the light pen with different postures are collected while the probe tip is kept in firm contact with a reference conical hole. The probe tip position is determined by computing the rotation matrix and translation vector from the obtained images by using the least square fitting method. The experimental results demonstrate the effectiveness of the proposed approach. Its repeatability reaches 0.033 mm, 0.030 mm, and 0.043 mm in x, y, and z axes, respectively, and its convergence speed is satisfactory.
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