A gear-linkage quaternion joint based cable-driven serpentine manipulator: Structural design, kinematics, and motion planning

Cable-driven serpentine manipulators exhibit significant potential for confined-space operations owing to their slender structure and dexterous motion capability. However, their practical application is often limited by the trade-off between structural complexity (due to excessive actuators) and flexibility. To address this problem, a novel gear-linkage quaternion joint mechanism is proposed in this study to reduce the actuator count while preserving maneuverability. Based on this mechanism, path planning research for this manipulator is carried out to verify its operation capability in narrow spaces. An improved Gaussian sampling based probabilistic roadmap (PRM) method is introduced to enhance path planning efficiency for complex three-dimensional configurations in constrained environments. Furthermore, to ensure precise navigation, a nonlinear optimization based path-following control method is developed, enabling serpentine manipulators to follow predefined paths in narrow spaces. Finally, the experimental system is built. Experimental results demonstrate that the manipulator, with fewer actuators, achieves superior detection capability in narrow-space exploration.