Kamran ShamaeiYale University
Mechanical Engineering
Subject-Specific Predictive Models of Lower-limb Joint Quasi-Stiffness and Applications in Exoskeleton Design
Kamran ShamaeiProf. Gregory S. Sawicki
Prof. Aaron M. Dollar
Kamran ShamaeiYale University
Mechanical Engineering
Ankle-Foot Prosthesis from MIT (fig. from MIT news)
Ankle-Foot Prosthesis from U. Michigan
(fig. from PLoS One)
Scope and Application: Prostheses and Orthoses
HULC from UC Berkeley
C-Leg from Ottobock Underactuated Exosksleton from MIT (fig. from
scientificamerican.com)
Compliant SC Orthosis from Yale
Kamran ShamaeiYale University
Mechanical Engineering
Challenge: How to size the components of these devices for a
specific user size and gait speed?
Kamran ShamaeiYale University
Mechanical Engineering
Common Approach: Use average values for joint stiffnesses obtained
from gait lab data for a randomized sample population
Kamran ShamaeiYale University
Mechanical Engineering
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
Kamran ShamaeiYale University
Mechanical Engineering
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
Kamran ShamaeiYale University
Mechanical Engineering
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
Kamran ShamaeiYale University
Mechanical Engineering
Alternative Framework
Kamran ShamaeiYale University
Mechanical Engineering
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.
Kamran ShamaeiYale University
Mechanical Engineering
Linear Moment-Angle Behavior of the Knee in Stance
Design: Compliantly support the knee by an exoskeletal springShamaei et al., PLoS One 2013aShamaei et al., ICORR 2011
Kamran ShamaeiYale University
Mechanical Engineering
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.
Kamran ShamaeiYale University
Mechanical Engineering
Challenge: How to size the spring for a specific user and gait speed?
K (Nm/rad)~ [80 , 800]Shamaei et al. (2013) PLoS One
Kamran ShamaeiYale University
Mechanical Engineering
Linear Moment-Angle Behavior of the Knee in Stance, a Closer Look
Tune the stiffness of the device according to the body size and gait speed
K is:• User-specific• Gait-specific
(Shamaei, ICORR 2011)
Kf
Ke
K
Kamran ShamaeiYale University
Mechanical Engineering
Framework : Mathematical/Statistical models that estimate knee quasi-stiffnesses using a set of
measurable parameters
Gait SpeedWeightHeight
Joint Excursion
Kf
Ke
K
Kamran ShamaeiYale University
Mechanical Engineering
Start with Inverse Dynamics Analysis
MAnkle ,FAnkle
MKnee
GRF, GRM
Kamran ShamaeiYale University
Mechanical Engineering
Linking to Gait and Body ParametersMKnee
MKnee~ f(W,V,H)
MKnee~ Kiθi
Ki ~ f(WVH/θi -WV/θi - WH/θi - W/θi - 1/θi - WVH- WH)
Kf
Ke
Kamran ShamaeiYale University
Mechanical Engineering
Statistical Analysis
Regression on Experimental Data
Ki ~ f(WVH/θi, WV/θi, WH/θi,
W/θi, 1/θi, WVH, WH)
Kamran ShamaeiYale University
Mechanical Engineering
Springy Behavior at the Optimal Gait Speed
Support the knee using a spring
Kamran ShamaeiYale University
Mechanical Engineering
Adjust the Stiffness at Higher Gait Speeds
Assist the knee using a combination of a spring and an active component
Kamran ShamaeiYale University
Mechanical Engineering
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.
Kamran ShamaeiYale University
Mechanical Engineering
From: Shamaei K, Sawicki G, and Dollar A. Estimation of Quasi-Stiffness of the Human Hip in the Stance Phase of Walking, in review.
Moment-Angle Performance of Hip
Kamran ShamaeiYale University
Mechanical Engineering
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.
Kamran ShamaeiYale University
Mechanical Engineering
Similar Approach for Hip and Ankle
MAnkle ,FAnkle
Mknee , FKnee
GRF, GRM
MHip
• Quasi-Stiffness• Work
• Quasi-Stiffness
Kamran ShamaeiYale University
Mechanical Engineering
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.
Kamran ShamaeiYale University
Mechanical Engineering
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.
Kamran ShamaeiYale University
Mechanical Engineering
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
Kamran ShamaeiYale University
Mechanical Engineering
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
Kamran ShamaeiYale University
Mechanical Engineering
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
Kamran ShamaeiYale University
Mechanical Engineering
Thanks for Your AttentionThanks 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
