Calibration of Concentric Tube Continuum Robots: Automatic Alignment of Precurved Elastic Tubes

Joint level calibration is an integral part of robotics as it directly influences the achievable accuracy. As opposed to serial robotic arms, continuum robots are not composed of any rigid links or joints, but of elastic materials that undergo bending and torsion. The jointless composition requires dedicated calibration procedures. In this letter, we introduce an automatic method for aligning precurved elastic tubes for joint level calibration of concentric tube continuum robots. The robot tip is equipped with a sensor in order to track its position during calibration such that subsequent data processing can extract the rotational zero position automatically. While we present a general framework independent of the utilized sensor technology, we evaluate our approach using three different sensing methodologies, i.e. magnetic, inductive, and electromagnetic. Furthermore, we advise on properties for appropriate sensors. Our experimental results show, that the rotational home position can be found reproducibly with a minimal dispersion of 0.011°.