Automatic Robot Calibration for the NAO

In this paper, we present an automatic approach for the kinematic calibration of the humanoid robot NAO. The kinematic calibration has a deep impact on the performance of a robot playing soccer, which is walking and kicking, and therefore it is a crucial step prior to a match. So far, the existing calibration methods are time-consuming and error-prone, since they rely on the assistance of humans. The automatic calibration procedure instead consists of a self-acting measurement phase, in which two checkerboards, that are attached to the robot's feet, are visually observed by a camera under several different kinematic configurations, and a final optimization phase, in which the calibration is formulated as a non-linear least squares problem, that is finally solved utilizing the Levenberg-Marquardt algorithm.