Enhancing Continuum Robot Mobility: Design and Control with Integrated Dual Rotational DOFs

Abstract

Continuum robots, known for their compliance in unstructured environments, face limitations due to the lack of rotational degrees of freedom (DOFs) about the backbone. This prevents them from compensating undesired torsional deformation and performing 6-DOF control of the end-effector, thereby restricting their mobility. This paper presents a continuum robot with integrated dual rotational DOFs. One is integrated at the arm base to compensate for torsional deformation caused by external loads, while the other one, located at the arm tip, enables full 6-DOF control of the end-effector. To control the robot, a screw-theory-based kinematic model and a kinematic control framework are proposed to enable real-time, simultaneous control of the end-effector’s position and orientation. Experimental results show that the arm base rotational joint can fully compensate for undesired torsional deformation caused by a 1000 g payload. Thanks to the arm tip’s DOF and the proposed kinematic control framework, the robot’s end-effector can maintain a constant orientation while achieving open-loop path-tracking errors of only 3.3% of the arm’s length (930 mm), and successfully executing valve-closing tasks with coordinated 6-DOF motion, demonstrating the robot’s potential for industrial maintenance, human-robot interaction, and confined-space manipulation.