Hand-Eye Calibratilon Using Active Vision

The project described in this paper designed and implemented a hand-eye calibration method for manipulators under observation by stereo cameras. This method has been utilized on Johnson Space Center´s Robonaut, and on a planetary manipulator mock-up at the Jet Propulsion Laboratory. The intent of this calibration is to improve the manipulator´s hand-eye coordination. The approach uses kinematic and stereo vision measurements, namely the joint angles self-reported by the arm and 3-D positions of a calibration fixture as measured by vision, to estimate the transformation from the arm´s base coordinate system to its hand coordinate system and to its vision coordinate system. In this formulation, the stereo measurements are assumed to be accurate, and any mismatches are absorbed in a modified model of the arm. These methods have shown to reduce mismatch between kinematically derived positions and visually derived positions on Robonaut Unit A from a mean of 13.75 cm to a mean of 1.85 cm. Improved performance in semi-autonomous tasks is also described. On JPL´s manipulator, with kinematics similar to that of the Mars Exploration Rover, the calibration reduced the mismatch from 15.26 mm to between 3 mm and 5.5 mm.