An Anthropomorphic Robotic Finger with Innate Human-Finger-Like Biomechanical Advantages Part II: Flexible Tendon Sheath and Grasping Demonstration

The human hand has a fantastic ability to interact with various objects in the dynamic unstructured environment of our daily activities. We believe that this outstanding performance benefits a lot from the unique biological features of the hand musculoskeletal system. In Part I of this article, a bio-inspired anthropomorphic robotic finger was developed, based on which two human-finger-like biomechanical advantages were elaborately investigated, including the anisotropic variable stiffness associ- ated with the ligamentous joints and the enlarged feasible force space associated with the reticular extensor mechanisms. In Part II, the fingertip force-velocity characteristics resulting from the flexible tendon sheath are studied. It indicates that the fingertip force–velocity workspace can be greatly augmented owing to the self-adaptive morphing of the flexible tendon sheaths, showing the average improvement of 41.2% theoretically and 117.5% exper- imentally compared with the results of 2 mm, 4 mm, and 6 mm size rigid tendon sheaths. Grasping tests and comparisons are then conducted with four three-fingered robotic hands (one with the robotic finger proposed in Part I, one with hinge joints, one with linear extensors, and one with rigid tendon sheaths) and the human hands of six subjects to handle various objects on flat, rough, and soft surfaces. The results show that the novel bio-inspired design in this research could improve the grasping success rates of the robotic hand. Compared with the grasping test results from the robotic hand with the bio-inspired robotic finger proposed in Part I, the Manuscript received 19 May 2022; accepted 16 July 2022. Date of publication 9 September 2022; date of current version 8 February 2023. This work was supported in part by the project of National Key R&D Program of China under Grant 2018YFC2001300 and in part by the project of National Natural Science Foundation of China under Grant 91948302, Grant 91848204, Grant 52005209, and Grant 51675222. This article recommended for publication by Associate Editor F. Ficuciello and Editor E. Yoshida upon evaluation of the reviewers’ comments. (Corresponding authors: Guowu Wei; Lei Ren.) Yiming Zhu is with the School of Mechanical, Aerospace and Civil Engineer- ing,The University of Manchester,Manchester M13 9PL,U.K.,and also with the College of Intelligence Science and Technology, National University of Defense Technology, Changsha 410073, China (e-mail: yiming.zhu@manchester.ac.uk). Guowu Wei is with the School of Science, Engineering and Environment, University of Salford, M5 4WT Salford, U.K. (e-mail: g.wei@salford.ac.uk). Lei Ren is with the School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, M13 9PL Manchester, U.K., and also with the Key Laboratory of Bionic Engineering, Ministry of Education, Jilin University, Changchun 130012, China (e-mail: lei.ren@manchester.ac.uk). Zirong Luo and Jianzhong Shang are with the College of Intelligence Science and Technology, National University of Defense Technology, Changsha 410073, China (e-mail: luozirong@nudt.edu.cn; jz_shang_nudt@163.com). This article has supplementary material provided by the au- thors and color versions of one or more figures available at https://doi.org/10.1109/TRO.2022.3200143. Digital Object Identifier 10.1109/TRO.2022.3200143 overall grasping performance of a robotic hand with hinge joints, linear extensors, and rigid tendon sheaths decreases by 10%, 6%, and17%,respectively.Theresultshavealsoshownthatwiththeem- bedded biomechanical advantages, even without complex control and sensory systems, the robotic fingers can achieve very compara- ble performance to human fingers in the grasping demonstrations presented, indicating average 94% of the success rate achieved by the human fingers. Successfully demonstrating 14 of 16 grasp types in the Cutkoskey taxonomy further shows the human-finger-like grasping capability of the proposed robotic fingers.