Multimode Composite Continuum Robot: Coupled Static Modeling and Verification

Hybrid continuum robots with concentric tubes and cable-driven mechanisms offer compactness and dexterity. However, they face limited adaptability and modeling challenges. This article proposes, for the first time, a multimode operation strategy for the composite continuum robot, enabling switching among high stiffness, high flexibility, and high precision modes. By adjusting the relative position between the concentric tube and the notched continuum, the robot achieves flexible transitions among these modes. A static model based on Euler–Bernoulli beam theory is established, where the bending moments from the concentric tube acting on the notched continuum segment are analytically integrated to reflect coupling effects. Algorithms are designed to achieve the mapping between the driving force and the shape, as well as the mapping relationship between the driving cable length and the robot shape. Based on the Kepler oval and the established static model, the inverse kinematics model of the robot is constructed. Simulations and experimental results show a modeling error of only 0.042 mm (0.084%), outperforming conventional models. The robot demonstrates convenient mode switching, showing performance characteristics, such as high stiffness, high flexibility, and high precision. This work contributes to improved modeling and control strategies for continuum robots.