A Novel Cable-Driven Manipulator with Constant-Curvature Deflections and Equal Displacements of the Antagonistic Cables

The constant-curvature method can effectively reduce the complexity in kinematic modeling of the cable-driven manipulator and make the dynamic control easier. However, existing research has encountered some difficulties in modeling using this method. Due to the external load, the bending shape is not a constant-curvature arc. In this paper, a novel cable-driven serpentine manipulator is proposed, which can bend in accurate constant curvature under situations with or without external load. This manipulator is mainly composed of two parts, including arm segments and links. Both are with gear teeth. Two adjacent segments have a rolling motion by gear meshing, connected by an auxiliary link. The accurate constant curvature is realized by gear meshing of the links. Moreover, through the delicate position distribution of the gear center, the driving cables have equal antagonistic displacements, which means that a single pulley can control both cables. This feature can reduce the number of actuators significantly. Besides, the mapping between driving cable space and joint space can be linearized with a relatively small error, thanks to the special structure. Experiments in different conditions are carried out and the results show that the maximum tracking error and repeat positioning error are 4.9 mm and 4.87 mm while the average values are 1.52 mm and 1.04 mm, which are very small compared to the 272 mm long manipulators.