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Journal of Healthcare Engineering
Volume 2017, Article ID 3850351, 6 pages
Research Article

Obtaining Natural Sit-to-Stand Motion with a Biomimetic Controller for Powered Knee Prostheses

Department of Mechanical Engineering, The University of Alabama, 286 Hardaway Hall, P.O. Box 870276, Tuscaloosa, AL 35487-0276, USA

Correspondence should be addressed to Xiangrong Shen;

Received 12 June 2017; Revised 8 August 2017; Accepted 9 August 2017; Published 18 September 2017

Academic Editor: Antonio Fernández-Caballero

Copyright © 2017 Molei Wu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Standing up from a seated position is a common activity in people’s daily life. However, for transfemoral (i.e., above-knee) amputees fitted with traditional passive prostheses, the sit-to-stand (STS) transition is highly challenging, due to the inability of the prosthetic joints in generating torque and power output. In this paper, the authors present a new STS control approach for powered lower limb prostheses, which is able to regulate the power delivery of the prosthetic knee joint to obtain natural STS motion similar to that displayed by healthy subjects. Mimicking the dynamic behavior of the knee in the STS, a unified control structure provides the desired control actions by combining an impedance function with a time-based ramp-up function. The former provides the gradual energy release behavior desired in the rising phase, while the latter provides the gradual energy injection behavior desired in the loading phase. This simple and intuitive control structure automates the transition between the two phases, eliminating the need for explicit phase transition and facilitating the implementation in powered prostheses. Human testing results demonstrated that this new control approach is able to generate a natural standing-up motion, which is well coordinated with the user’s healthy-side motion in the STS process.