Abstract
Current humanoid robots face persistent mechanical challenges in combining load-bearing capacity, dexterity, and compliance within compact structures, limiting their ability to perform versatile tasks and interact safely with humans. As the foundation of upper limb movement, the shoulder joint is critical to humanoid robots to perform manipulation, human-robot interaction, and other complex tasks. In this review, we outline the biological principle of human shoulder joints and critically review the research progress of robotic shoulder joints, with particular attention to their flexibility and stability. Based on the system architecture, we propose a clear taxonomy classifying robotic shoulder joints into drive-transmission integrated and drive-transmission separated systems, analyzing the benefits and drawbacks of different architectures. By comparing current robotic shoulder joints against the biological human shoulder joint, we ultimately identify core challenges and potential design trends for next-generation bionic shoulder joints intended for humanoid robots.
Keywords
References
-
2. Zhang C, Duan Y, Jiao Z, Zhu Y, Xu B, Yang H, et al. Functional fluid-based soft robotic actuation. Adv Mater. 2025;37(34):2502669.[DOI]
-
4. Lynch KM, Park FC. Modern Robotics: Mechanics, Planning, and Control [Internet]. Cambridge: Cambridge University Press; 2017.[DOI]
-
5. Craig JJ. Introduction to Robotics: Mechanics and Control 2009 [Internet]. Upper Saddle River, NJ: Pearson Prentice Hall; 2005. Available from: https://www.changjiangcai.com/files/text-books/Introduction-to-Robotics-3rd-edition.pdf
-
6. Yang H, Wei G, Ren L. Development and characteristics of a highly biomimetic robotic shoulder inspired by musculoskeletal mechanical intelligence. IEEE Trans Robot. 2024;40:2672-2691.[DOI]
-
7. Christoph CC, Kazemipour A, Vogt MR, Zhang Y, Katzschmann RK. Self-sensing feedback control of an electrohydraulic robotic shoulder. In: 2024 IEEE International Conference on Robotics and Automation (ICRA); 2024 May 13-17; Yokohama, Japan. Piscataway: IEEE; 2024. p. 4679-4685.[DOI]
-
8. Niiyama R. Soft actuation and compliant mechanisms in humanoid robots. Curr Robot Rep. 2022;3(3):111-117.[DOI]
-
9. Roychoudhury A, Khorshidi S, Agrawal S, Bennewitz M. Perception for humanoid robots. Curr Robot Rep. 2023;4(4):127-140.[DOI]
-
10. Lai JC, Kim E, Xu C, Niu S, Jiang Y, Zhong D, et al. A skin-inspired high-κ self-healing polymer for low-voltage dielectric elastomer actuators. Adv Mater. 2026;38(56):e23659.[DOI]
-
13. Li N, Zhan F, Guo M, Yuan X, Chen X, Li Y, et al. Fingertip-inspired spatially anisotropic inductive liquid metal sensors with ultra-wide range, high linearity and exceptional stability. Adv Mater. 2025;37(19):2419524.[DOI]
-
15. Hsieh HC, Chen DF, Chien L, Lan CC. Design of a parallel actuated exoskeleton for adaptive and safe robotic shoulder rehabilitation. IEEE/ASME Trans Mechatron. 2017;22(5):2034-2045.[DOI]
-
16. Gray J. Gray’s Anatomy. Anchor Canada; 2010.
-
19. Chen W, Xiong C, Wang Y. Analysis and synthesis of underactuated compliant mechanisms based on transmission properties of motion and force. IEEE Trans Robot. 2020;36(3):773-788.[DOI]
-
20. Gasbarro G, Bondow B, Debski R. Clinical anatomy and stabilizers of the glenohumeral joint. Ann Joint. 2017;2(10):58.[DOI]
-
24. Provenzano P, Lakes R, Keenan T, vnderby R. Nonlinear ligament viscoelasticity. Ann Biomed Eng. 2001;29(10):908-914.[DOI]
-
26. Alexander S, Southgate DFL, Bull AMJ, Wallace AL. The role of negative intraarticular pressure and the long head of biceps tendon on passive stability of the glenohumeral joint. J Shoulder Elbow Surg. 2013;22(1):94-101.[DOI]
-
27. Kumar VP, Balasubramaniam P. The role of atmospheric pressure in stabilising the shoulder. An experimental study. J Bone Joint Surg Br. 1985;67-B(5):719-721.[DOI]
-
30. Schmidt TA, Gastelum NS, Nguyen QT, Schumacher BL, Sah RL. Boundary lubrication of articular cartilage: Role of synovial fluid constituents. Arthritis Rheum. 2007;56(3):882-891.[DOI]
-
31. Klein J. Molecular mechanisms of synovial joint lubrication. Proc Inst Mech Eng Part J J Eng Tribol. 2006;220(8):691-710.[DOI]
-
34. Véronneau C, Denis J, Lhommeau P, St-Jean A, Girard A, Plante JS, et al. Modular magnetorheological actuator with high torque density and transparency for the collaborative robot industry. IEEE Robot Autom Lett. 2023;8(2):896-903.[DOI]
-
35. Liu C, Chang WJ, Lin PC. Development of a 2-DOF spherical joint with extended range of motion achieves continuous rotation. Mech Mach Theory. 2022;177:105057.[DOI]
-
36. Abe K, Tadakuma K, Tadakuma R. ABENICS: Active ball joint mechanism with three-DoF based on spherical gear meshings. IEEE Trans Robot. 2021;37(5):1806-1825.[DOI]
-
37. Liang G, Zong L, Lam TL. DISG: Driving-integrated spherical gear enables singularity-free full-range joint motion. IEEE Trans Robot. 2023;39(6):4464-4481.[DOI]
-
38. Mghames S, Catalano MG, Bicchi A, Grioli G. A spherical active joint for humanoids and humans. IEEE Robot Autom Lett. 2019;4(2):838-845.[DOI]
-
39. Patel VV, Dollar AM. Combining grasping and rotation with a spherical robot hand mechanism. Nat Mach Intell. 2025;7(7):999-1009.[DOI]
-
40. Gealy DV, McKinley S, Yi B, Wu P, Downey PR, Balke G, et al. Quasi-direct drive for low-cost compliant robotic manipulation. In: 2019 International Conference on Robotics and Automation (ICRA); 2019 May 20-24; Montreal, QC, Canada. Piscataway: IEEE; 2019. p. 437-443.[DOI]
-
41. Ostyn F, Vanderborght B, Crevecoeur G. Series clutched actuation for collision-tolerant high-speed robots. J Mech Robot. 2024;16(12):121008.[DOI]
-
42. Tsai LW. Robot Analysis: The Mechanics of Serial and Parallel Manipulators [Internet]. New York: John Wiley & Sons; 1999.
-
43. Li G, Liang X, Gao Y, Su T, Liu Z, Hou ZG. A linkage-driven underactuated robotic hand for adaptive grasping and in-hand manipulation. IEEE Trans Autom Sci Eng. 2024;21(3):3039-3051.[DOI]
-
44. Lilge S, Nuelle K, Childs JA, Wen K, Rucker DC, Burgner-Kahrs J. Parallel-continuum robots: A survey. IEEE Trans Robot. 2024;40:3252-3270.[DOI]
-
45. Gosselin C, Schreiber LT. Redundancy in parallel mechanisms: A review. Appl Mech Rev. 2018;70(1):010802.[DOI]
-
46. Tian Q, Flores P, Lankarani HM. A comprehensive survey of the analytical, numerical and experimental methodologies for dynamics of multibody mechanical systems with clearance or imperfect joints. Mech Mach Theory. 2018;122:1-57.[DOI]
-
47. Tsai MJ, Lai TH. Kinematic sensitivity analysis of linkage with joint clearance based on transmission quality. Mech Mach Theory. 2004;39(11):1189-1206.[DOI]
-
48. López-Martínez J, Blanco-Claraco JL, García-Vallejo D, Giménez-Fernández A. Design and analysis of a flexible linkage for robot safe operation in collaborative scenarios. Mech Mach Theory. 2015;92:1-16.[DOI]
-
50. Huang Q, Dong C, Yu Z, Chen X, Li Q, Chen H, et al. Resistant compliance control for biped robot inspired by humanlike behavior. IEEE/ASME Trans Mechatron. 2022;27(5):3463-3473.[DOI]
-
52. Lin S, Li J, Li J, Liu T, Gu Y, Jiang Y, et al. Upper limb posture-based control of a tendon-driven robotic arm integrated with a wheelchair for activities of daily living. In: 2025 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM); 2025 July 14-18; Hangzhou, China. Piscataway: IEEE; 2025. p. 1-6.[DOI]
-
54. Lin Z, Shao Q, Liu XJ, Zhao H. An anthropomorphic musculoskeletal system with soft joint and multifilament pneumatic artificial muscles. Adv Intell Syst. 2022;4(10):2200126.[DOI]
-
55. Sharma B, Davies J, Nicotra E, Ji A, Zhu K, Phan PT, et al. A soft robotic textile-actuated anthropomorphic artificial shoulder mechanism. Adv Intell Syst. 2025;7(4):2400807.[DOI]
-
56. Lin YH, Liu CS, Yeh CN. Design and simulation of novel 3-DOF spherical voice coil motor. Actuators. 2021;10(7):155.[DOI]
-
57. Bai K, Chen W, Lee KM, Que Z, Huang R. Spherical wrist with hybrid motion-impedance control for enhanced robotic manipulations. IEEE Trans Robot. 2022;38(2):1174-1185.[DOI]
-
58. Li M, Xiao Q, Wang Z, Liu C, Bai K. A variable stiffness spherical joint motor by magnetic energy shaping. IEEE Trans Robot. 2024;40:1410-1420.[DOI]
-
59. Zhao D, Wang X, Wei F, Ren L, Wang K, Ren L. The design and control of a proprioceptive modular actuator for tendon-driven robots. Actuators. 2025;14(6):278.[DOI]
-
60. Kirchhoff J, von Stryk O. New insights in synthetic fiber rope elongation and its detection for ultra lightweight tendon driven series elastic robots. In: 2017 IEEE International Conference on Advanced Intelligent Mechatronics (AIM); 2017 July 3-7; Munich, Germany. Piscataway: IEEE; 2017. p. 64-69.[DOI]
-
61. Nguyen VP, Chow WT, Dhyan SB, Zhang B, Han BS, Wong HYA. Low-cost cable-driven robot arm with low-inertia movement and long-term cable durability. Robotics. 2024;13(9):128.[DOI]
-
62. Horigome A, Endo G. Investigation of repetitive bending durability of synthetic fiber ropes. IEEE Robot Autom Lett. 2018;3(3):1779-1786.[DOI]
-
63. Yousaf SN, Mukherjee G, King R, Deshpande AD. Experimental and simulation-based estimation of interface power during physical human-robot interaction in hand exoskeletons. IEEE Robot Autom Lett. 2024;9(3):2575-2581.[DOI]
-
64. Lens T, von Stryk O. Investigation of safety in human-robot-interaction for a series elastic, tendon-driven robot arm. In: 2012 IEEE/RSJ International Conference on Intelligent Robots and Systems; 2012 Oct 7-12; Vilamoura-Algarve, Portugal. Piscataway: IEEE; 2012. p. 4309-4314.[DOI]
-
65. Kang BS, Kothera CS, Woods BKS, Wereley NM. Dynamic modeling of Mckibben pneumatic artificial muscles for antagonistic actuation. In: Proceedings of the 2009 IEEE International Conference on Robotics and Automation; 2009 May 12; Kobe, Japan. Piscataway: IEEE; 2009. p. 643-648.[DOI]
-
66. Rus D, Tolley MT. Design, fabrication and control of soft robots. Nature. 2015;521(7553):467-475.[DOI]
-
67. Tondu B, Ippolito S, Guiochet J, Daidie A. A seven-degrees-of-freedom robot-arm driven by pneumatic artificial muscles for humanoid robots. Int J Robot Res. 2005;24(4):257-274.[DOI]
-
68. Xavier MS, Tawk CD, Zolfagharian A, Pinskier J, Howard D, Young T, et al. Soft pneumatic actuators: A review of design, fabrication, modeling, sensing, control and applications. IEEE Access. 2022;10:59442-59485.[DOI]
-
69. Feng M, Yang D, Ren L, Wei G, Gu G. X-crossing pneumatic artificial muscles. Sci Adv. 2023;9(38):eadi7133.[DOI]
-
70. Shen X. Nonlinear model-based control of pneumatic artificial muscle servo systems. Control Eng Pract. 2010;18(3):311-317.[DOI]
-
71. Dai S, Li S, Ji W, Wang R, Liu S. Adaptive friction compensation control of robotic pneumatic end-effector based on LuGre model. Industrial Robot. 2023;50(5):848-860.[DOI]
-
72. Shi H, Tan K, Zhang B, Liu W. Review on research progress of hydraulic powered soft actuators. Energies. 2022;15(23):9048.[DOI]
-
73. Greco C, Kotak P, Pagnotta L, Lamuta C. The evolution of mechanical actuation: From conventional actuators to artificial muscles. Int Mater Rev. 2022;67(6):575-619.[DOI]
-
74. Sharma B, Nicotra E, Davies J, Nguyen CC, Phan PT, Ji A, et al. Compliance control with dynamic and self-sensing hydraulic artificial muscles for wearable assistive devices. In: 2025 IEEE International Conference on Robotics and Automation (ICRA); 2025 May 19-23; Atlanta, GA, USA. Piscataway: IEEE; 2025. p. 3393-3399.[DOI]
-
76. Feng Y, Ide T, Nabae H, Endo G, Sakurai R, Ohno S, et al. Safety-enhanced control strategy of a power soft robot driven by hydraulic artificial muscles. ROBOMECH J. 2021;8(1):10.[DOI]
-
77. Wensing PM, Wang A, Seok S, Otten D, Lang J, Kim S. Proprioceptive actuator design in the MIT cheetah: Impact mitigation and high-bandwidth physical interaction for dynamic legged robots. IEEE Trans Robot. 2017;33(3):509-522.[DOI]
-
78. Shah JA, Miller SR, Jernigan SR, Buckner GD. A permanent magnet synchronous spherical motor for high-mobility servo-actuation. Machines. 2022;10(8):612.[DOI]
-
79. Sun Z, Xu Y, Wang Q, Xu J, Li G, Wen Y. Design and identification of lumped-parameter thermal network model for real-time temperature estimation of permanent-magnet spherical motors. Therm Sci Eng Prog. 2023;44:102047.[DOI]
-
81. Abbott JJ, Diller E, Petruska AJ. Magnetic methods in robotics. Annu Rev Control Robot Auton Syst. 2020;3(1):57-90.[DOI]
-
82. Zabihollah S, Moezi SA, Sedaghati R. Design optimization of a miniaturized pneumatic artificial muscle and experimental validation. Actuators. 2023;12(6):221.[DOI]
-
84. Dempster WT. Space requirements of the seated operator, geometrical, kinematic, and mechanical aspects of the body with special reference to the limbs . Wright-Patterson Air Force Base, Ohio: Wright Air Development Center, Air Research and Development Command, United States Air Force; 1955. Available from: https://scispace.com/pdf/space-requirements-of-the-seated-operator-geometrical-1lhd7g9x4n.pdf
-
85. Kelkar R, Wang VM, Flatow EL, Newton PM, Ateshian GA, Bigliani LU, et al. Glenohumeral mechanics: A study of articular geometry, contact, and kinematics. J Shoulder Elbbow Surg. 2001;10(1):73-84.[DOI]
-
86. Koga Y, Kawaharazuka K, Toshimitsu Y, Nishiura M, Omura Y, Asano Y, et al. Self-body image acquisition and posture generation with redundancy using musculoskeletal humanoid shoulder complex for object manipulation. IEEE Robot Autom Lett. 2021;6(4):6686-6692.[DOI]
-
89. Fam H, Bryant JT, Kontopoulou M. Rheological properties of synovial fluids. Biorheology. 2007;44(2):59-74.[DOI]
-
90. Crosbie J, Kilbreath SL, Hollmann L, York S. Scapulohumeral rhythm and associated spinal motion. Clin Biomech. 2008;23(2):184-192.[DOI]
Copyright
© The Author(s) 2026. This is an Open Access article licensed under a Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, sharing, adaptation, distribution and reproduction in any medium or format, for any purpose, even commercially, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Publisher’s Note
Share And Cite


