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Logo for the Journal of Rehab R&D
Volume 42 Number 3, May/June 2005
Pages 327 — 342

Abstract - The effects of static friction and backlash on extended physiological proprioception control of a powered prosthesis

Todd R. Farrell, MS;1,3* Richard F. Weir, PhD;1-3 Craig W. Heckathorne, MS;3 Dudley S. Childress, PhD1-3

1Department of Biomedical Engineering, McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL; 2Jesse Brown VA Medical Center; Chicago, IL; 3Northwestern University Prosthetics Research Laboratory and Rehabilitation Engineering Research Center, Chicago, IL
Abstract — In general, externally powered prostheses do not provide proprioceptive feedback and thus require the user to rely on cognitively expensive visual feedback to effectively control the prosthesis. Applying the concept of extended physiological proprioception (EPP) to externally powered prostheses provides direct feedback to the user's proprioceptive system regarding the position, velocity, and forces applied to the prosthesis. However, electric elbows with EPP controllers developed at the Northwestern University Prosthetics Research Laboratory have exhibited unexplained "jerky" behavior in both clinical fittings and bench-top operation. In addition, the development of limit cycles, a specific type of constant-amplitude oscillation, had been observed in bench-top use of these elbows. Backlash and static friction within the EPP system were found to be primarily responsible for the development of limit cycles. Reducing static friction and backlash improved the system's performance. These results suggest that to most effectively implement EPP, prosthesis manufacturers should design prosthetic components that minimize static friction and backlash.
Key words: backlash, control, EPP, extended physiological proprioception, friction, limit cycles, nonlinearities, prosthesis, prosthetics, upper limb.

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