Design, Development, and Validation of a Lightweight Nonbackdrivable Robotic Ankle Prosthesis

Tommaso Lenzi*, Marco Cempini, Levi J Hargrove, Todd A Kuiken

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


Robotic ankle prostheses can imitate the biomechanical function of intact legs at the cost of a larger weight and size compared to conventional passive prostheses. Unfortunately, increased weight and size negatively affect comfort and socket stability, ultimately limiting their clinical viability. Alternatively, a nonbackdrivable transmission system can be used to actively regulate the ankle position during nonweight bearing activities only. This semiactive design can be made smaller and lighter as a result of the lower actuation power requirements. However, the transmission system must withstand high loads during stance and standing. Thus, available semiactive prostheses are still significantly heavier and have a larger build height than passive ankle prostheses. In this paper, we present the design, development, and validation of a semiactive ankle prosthesis with a nonbackdrivable cam-follower mechanism designed to lower the load on moving components and align with the foot longitudinally as necessary to reduce the prosthesis weight and size. The proposed ankle mechanism is ∼50% shorter, has ∼40% wider range of motion (ROM), and is estimated to be ∼27% lighter than available semiactive prostheses. Experiments with a transtibial subject show that the semiactive prosthesis can increase foot clearance up to 142% and reduce the load on the residual limb as low as 32% compared to passive prostheses.

Original languageEnglish (US)
Article number8610176
Pages (from-to)471-482
Number of pages12
JournalIEEE/ASME Transactions on Mechatronics
Issue number2
StatePublished - Apr 2019


  • Ankle-foot
  • design
  • nonbackdrivable
  • prosthesis
  • robotics
  • transmission
  • transtibial amputee

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Computer Science Applications
  • Electrical and Electronic Engineering


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