Precise Calibration of Robots with small link lengths using Kinematic Extensions

Complex anthropomorphic robotic hands with small link lengths and large number of degrees of freedom pose a unique challenge for calibration. The problem is interesting because the small magnitude of joint motion produced by small robots are difficult to capture by external sensors such as motion tracking systems. There is a need for a simple yet effective solution to this problem. In this paper, we show that a simple mechanical extension of the kinematic chain can be utilized to address this issue with good results. Using Standard motion tracking system and least squares optimization techniques, we identify joint sensor parameters. We also use finger tip loop closure distance, which is the distance between the thumb finger tip and the rest of the finger tips taken individually as an aid in estimating the true joint angles to calibrate the joint position sensors mounted on the hand. The results obtained are a significant improvement over the manual sensor calibration.