Curvature, Torsion, and Force Sensing in Continuum Robots Using Helically Wrapped FBG Sensors

Due to their small size and flexibility, fiber Bragg grating (FBG) sensors have been integrated into needle-sized continuum robots for shape estimation and force measurement. The challenge in extending previous shape and force sensing technologies to pre-curved continuum robots, such as concentric-tube robots, is that torsion information is essential for accurate shape estimation, and the force-strain relationship is nonlinear. In this letter, a novel helically wrapped FBG sensor design and corresponding force-curvature-strain model are developed to provide simultaneous curvature, torsion, and force measurement. To validate this design and modeling technique, two sensorized Nitinol tubes were fabricated and tested in an experimental setup. The results showed that accurate and sensitive curvature, torsion, and force measurements can be obtained at a 100 Hz sampling rate.