Design of a Novel Compact Adaptive Ankle Exoskeleton for Walking Assistance

  • Yixin Shao
  • Wuxiang ZhangEmail author
  • Kun Xu
  • Xilun Ding
Conference paper
Part of the Mechanisms and Machine Science book series (Mechan. Machine Science, volume 73)


Series elastic actuators (SEAs) are commonly used in ankle exoskeletons for friendly human-robot interaction and high power efficiency. However, most ankle exoskeletons face a common performance limitation due to the use of fixed stiffness series springs. In this paper, we present an adaptive ankle exoskeleton for walking assistance. A novel compact variable stiffness SEA with a non-linear spring, which is able to passively change the spring stiffness as a function of output load, is developed to overcome the limitation of the conventional SEAs. The predefined nonlinear elasticity of the proposed passively variable stiffness SEA (pVS-SEA) is achieved with a cam mechanism and leaf springs, which result in a compact design. Furthermore, a variable transmission mechanism is adopted to modulate the physical exoskeleton stiffness as a function of ankle joint angle. The exoskeleton mechanism is optimized based on the human gait data by employing a genetic algorithm. The results show that the presented ankle exoskeleton is adaptable under different walking conditions, and the energy efficiency of the system is improved compared with the conventional ones.


Ankle Exoskeleton Series Elastic Actuator (SEA) Nonlinear Spring Power Efficiency Design Optimization 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.



This research is supported by the National Natural Science Foundation of China (NSFC) under grant No. 91848104, and the National Key R&D Program of China under grant No. 2016YFE0105000.


  1. 1.
    Mooney LM, Herr HM: Biomechanical walking mechanisms underlying the metabolic reduction caused by an autonomous exoskeleton. J Neuroeng Rehabil 13, 1-12 (2016).Google Scholar
  2. 2.
    Collins SH, Wiggin MB, Sawicki GS: Reducing the energy cost of human walking using an unpowered exoskeleton. Nature 522, 212-215 (2015).Google Scholar
  3. 3.
    Diller S, Majidi C, Collins SH: A lightweight, low-power electroadhesive clutch and spring for exoskeleton actuation. In: IEEE International Conference on Robotics and Automation. p 682-689 (2016).Google Scholar
  4. 4.
    Witte KA, Zhang J, Jackson RW et al.: Design of two lightweight, high-bandwidth torque-controlled ankle exoskeletons. In: IEEE International Conference on Robotics and Automation. p 1223-1228 (2015).Google Scholar
  5. 5.
    Moltedo M, Bacek T, Verstraten T et al.: Powered ankle-foot orthoses: the effects of the assistance on healthy and impaired users while walking. J Neuroeng Rehabil 15, 1-25 (2018).Google Scholar
  6. 6.
    Chen G, Qi P, Guo Z et al.: Mechanical design and evaluation of a compact portable knee–ankle–foot robot for gait rehabilitation. Mechanism and Machine Theory 103, 51-64 (2016).Google Scholar
  7. 7.
    Van Dijk W, Meijneke C, Van Der Kooij H: Evaluation of the Achilles Ankle Exoskeleton. IEEE Trans Neural Syst Rehabil Eng 25, 151-160 (2017).Google Scholar
  8. 8.
    Choi H, Park YJ, Seo K et al.: A Multifunctional Ankle Exoskeleton for Mobility Enhancement of Gait-Impaired Individuals and Seniors. IEEE Robotics and Automation Letters 3, 411-418 (2018).Google Scholar
  9. 9.
    Hollander KW, Ilg R, Sugar TG et al.: An efficient robotic tendon for gait assistance. J Biomech Eng 128, 788-791 (2006).Google Scholar
  10. 10.
    Pratt GA, Williamson MM: Series elastic actuators. In: IEEE/RSJ International Conference on Intelligent Robots and Systems. IEEE, p 399-406 (1995).Google Scholar
  11. 11.
    Yu H, Huang S, Chen G et al.: Control design of a novel compliant actuator for rehabilitation robots. Mechatronics 23, 1072-1083 (2013).Google Scholar
  12. 12.
    Vanderborght B, Albu-Schäffer A, Bicchi A et al.: Variable impedance actuators: A review. Robotics and autonomous systems 61, 1601-1614 (2013).Google Scholar
  13. 13.
    Verstraten T, Geeroms J, Mathijssen G et al.: Optimizing the power and energy consumption of powered prosthetic ankles with series and parallel elasticity. Mechanism and Machine Theory 116, 419-432 (2017).Google Scholar
  14. 14.
    Cui L, Perreault EJ, Maas H et al.: Modeling short-range stiffness of feline lower hindlimb muscles. Journal of Biomechanics 41, 1945-1952 (2008).Google Scholar
  15. 15.
    Pfeifer S, Vallery H, Hardegger M et al.: Model-based estimation of knee stiffness. IEEE Trans Biomed Eng 59, 2604-2612 (2012).Google Scholar
  16. 16.
    Migliore SA, Brown EA, Deweerth SP: Novel Nonlinear Elastic Actuators for Passively Controlling Robotic Joint Compliance. Journal of Mechanical Design 129, 406-412 (2007).Google Scholar
  17. 17.
    Awtar S, Slocum AH, Sevincer E: Characteristics of beam-based flexure modules. Journal of Mechanical Design 129, 625-639 (2007).Google Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Yixin Shao
    • 1
    • 2
  • Wuxiang Zhang
    • 1
    • 2
    Email author
  • Kun Xu
    • 1
    • 2
  • Xilun Ding
    • 1
    • 2
  1. 1.School of Mechanical Engineering and AutomationBeihang UniversityBeijingChina
  2. 2.Beijing Advanced Innovation Center for Biomedical EngineeringBeihang UniversityBeijingChina

Personalised recommendations