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Subject-Specific Predictive Models for Lower-Limb Joint Quasi-Stiffness

Explore advanced models predicting joint stiffness for designing prostheses and exoskeletons, avoiding drawbacks of traditional methods. Enhance user-specific adjustments for better device fitting and gait support.

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Subject-Specific Predictive Models for Lower-Limb Joint Quasi-Stiffness

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  1. Subject-Specific Predictive Models of Lower-limb Joint Quasi-Stiffness and Applications in Exoskeleton Design Kamran Shamaei Prof. Gregory S. Sawicki Prof. Aaron M. Dollar

  2. Scope and Application: Prostheses and Orthoses UnderactuatedExosksleton from MIT (fig. from scientificamerican.com) C-Leg from Ottobock Compliant SC Orthosis from Yale HULC from UC Berkeley Ankle-Foot Prosthesis from U. Michigan (fig. from PLoS One) Ankle-Foot Prosthesis from MIT (fig. from MIT news)

  3. Challenge: How to size the components of these devices for a specific user size and gait speed?

  4. Common Approach: Use average values for joint stiffnesses obtained from gait lab data for a randomized sample population

  5. Drawbacks • Sample population body stature is not necessarily representative of the user’s • Costly and time-consuming • Design centers usually do not have a gait lab

  6. Drawbacks • Sample population body stature is not necessarily representative of the user’s • Costly and time-consuming • Design centers usually do not have a gait lab

  7. Drawbacks • Sample population body stature is not necessarily representative of the user’s • Costly and time-consuming • Design centers usually do not have a gait lab

  8. Alternative Framework

  9. Design Example: A Quasi-Passive Knee Exoskeleton Shamaei K, Napolitano P., and Dollar A. (2013) A Quasi-Passive Compliant Stance Control Knee-Ankle-Foot Orthosis, ICORR, Seattle, Washington, USA.

  10. Linear Moment-Angle Behavior of the Knee in Stance Design: Compliantly support the knee by an exoskeletal spring Shamaei et al., PLoS One 2013a Shamaei et al., ICORR 2011

  11. Yale Quasi-Passive Stance Control Orthosis Shamaei K, Napolitano P., and Dollar A. (2013) A Quasi-Passive Compliant Stance Control Knee-Ankle-Foot Orthosis, ICORR, Seattle, Washington, USA.

  12. K (Nm/rad)~ [80 , 800] Shamaei et al. (2013) PLoS One Challenge: How to size the spring for a specific user and gait speed?

  13. Linear Moment-Angle Behavior of the Knee in Stance, a Closer Look • K is: • User-specific • Gait-specific • (Shamaei, ICORR 2011) Ke K Kf Tune the stiffness of the device according to the body size and gait speed

  14. Framework: Mathematical/Statistical models that estimate knee quasi-stiffnesses using a set of measurable parameters Gait Speed Weight Height Joint Excursion Kf Ke K

  15. Start with Inverse Dynamics Analysis MKnee MAnkle ,FAnkle GRF, GRM

  16. Linking to Gait and Body Parameters MKnee MKnee~ Kiθi MKnee~ f(W,V,H) Ke Kf Ki~ f(WVH/θi-WV/θi- WH/θi- W/θi- 1/θi- WVH- WH)

  17. Statistical Analysis Regression on Experimental Data Ki ~ f(WVH/θi, WV/θi, WH/θi, W/θi, 1/θi, WVH, WH)

  18. Springy Behavior at the Optimal Gait Speed Support the knee using a spring

  19. Adjust the Stiffness at Higher Gait Speeds Assist the knee using a combination of a spring and an active component

  20. Comparison with Models that Use Average Values From: Shamaei K, Sawicki G, and Dollar A. (2013) Estimation of Quasi-Stiffness of the Human Knee in the Stance Phase of Walking, PLOS ONE.

  21. Moment-Angle Performance of Hip From: Shamaei K, Sawicki G, and Dollar A. Estimation of Quasi-Stiffness of the Human Hip in the Stance Phase of Walking, in review.

  22. Moment-Angle Performance of Ankle From: Shamaei K, Sawicki G, and Dollar A. (2013) Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking, PLOS ONE.

  23. Similar Approach for Hip and Ankle MHip • Quasi-Stiffness Mknee, FKnee MAnkle ,FAnkle • Quasi-Stiffness • Work GRF, GRM

  24. Models for Ankle Quasi-Stiffness and Work From: Shamaei K, Sawicki G, and Dollar A. (2013) Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking, PLOS ONE.

  25. Models for Hip Quasi-Stiffness From: Shamaei K, Sawicki G, and Dollar A. Estimation of Quasi-Stiffness of the Human Hip in the Stance Phase of Walking, in review.

  26. Conclusions • Models accurately predict the stiffnesses compared with average values • Utilize these equations in design of exoskeletons and prostheses • Ideally adjust the stiffness of the device according to the gait speed

  27. Conclusions • Models accurately predict the stiffnesses compared with average values • Utilize these equations in design of exoskeletons and prostheses • Ideally adjust the stiffness of the device according to the gait speed

  28. Conclusions • Models accurately predict the stiffnesses compared with average values • Utilize these equations in design of exoskeletons and prostheses • Ideally adjust the stiffness of the device according to the gait speed

  29. Thanks for Your Attention • Experimental data: • 26 subjects • 216 gait cycles • Gait speed (m/s): [0.75 , 2.63] • Height (m): [1.45 , 1.86] • Weight (kg): [57.7 , 94.0] • Data granted by: Prof. DeVita, Prof. Sawicki, and Prof. Frigo • Funding: US Defense Medical Research and Development Program, grant #W81XWH-11-2-0054

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