Decoupling Design and Fast Kinematics Resolving Method for Cable-Driven Segmented Manipulator

Abstract

A cable-driven segmented manipulator (CDSM) has considerable potential in narrow space operations because it has a slender and light body with flexible mobility. However, the existing CDSM segment driving mechanisms are coupled to each other. The driving distance of the rear segment cable is superimposed with that of the front segment cable, which renders the cables’ drive distance inconsistent. Moreover, the system kinematics, dynamics, and control become extremely complex. In this article, a novel decoupling driving mechanism is proposed to solve the coupling problem, simplifying the modeling and control of the CDSM. The routing of the driving cable is designed based on the characteristics of the symmetrical offset (i.e., the same magnitude but opposite in direction) of the cable length applicable to joints with one and two degrees of freedom. By modifying the direction of the driving cable in the middle of the proximal segment, the driving cable length of the distal segment is unaffected by the change of the angle of the front segment. Moreover, to increase the drive stroke, a multiturn winding mechanism is designed, reducing the volume and mass of the driving box. Accordingly, an improved forward and backward reaching inverse kinematics is proposed for CDSM based on virtual joints. Compared with the Jacobian pseudo-inverse method, the computational efficiency is improved. Finally, the proposed mechanisms and methods are verified via a CDSM prototype. The results indicate that the proposed manipulator compared with typical manipulators has larger movement range, higher end velocity, and guaranteed accuracy due to the proposed decoupled driving and fast kinematics resolution.