Hand-eye calibration and its accuracy analysis in robotic grinding

Hand-eye calibration that establishes the pose relationship between a robot and a laser scanner is one of the most critical tasks in robotic grinding. Calibration accuracy can significantly affect the geometry and dimensional accuracy of parts such as blades. In this paper, a hand-eye calibration approach is proposed using a standard sphere as the calibration object. More important, three valid ways to improve the calibration accuracy are given. First, based on lots of experiment data, it´s found that the scanning accuracy is related to the scanning area on the sphere. Combining error synthesis theory, an appropriate scanning area is found to improve the positioning accuracy of the sphere center. Second, we proved that moving along XYZ coordinate axes are best for robot during calibration process. Third, a novel orthogonalization algorithm of the calibrated rotation matrix is presented using differential kinematics. Different from the traditional orthogonalization algorithm, the algorithm converts the multiple solutions to a optimal approximate orthogonal solution, which avoids many unstable factors. Finally, test experiments show that the calibration accuracy is up to 0.0573mm. The calibration approach can be applied in robotic grinding of nuclear blades, aviation blades and turbine blades.