DocumentCode :
80226
Title :
The Difference Between Stiffness and Quasi-Stiffness in the Context of Biomechanical Modeling
Author :
Rouse, Elliott J. ; Gregg, Robert D. ; Hargrove, Levi J. ; Sensinger, J.W.
Author_Institution :
Dept. of Biomed. Eng., Northwestern Univ., Evanston, IL, USA
Volume :
60
Issue :
2
fYear :
2013
fDate :
Feb. 2013
Firstpage :
562
Lastpage :
568
Abstract :
The ankle contributes the majority of mechanical power during walking and is a frequently studied joint in biomechanics. Specifically, researchers have extensively investigated the torque-angle relationship for the ankle during dynamic tasks, such as walking and running. The slope of this relationship has been termed the “quasi-stiffness.” However, over time, researchers have begun to interchange the concepts of quasi-stiffness and stiffness. This is an especially important distinction as researchers currently begin to investigate the appropriate control systems for recently developed powered prosthetic legs. The quasi-stiffness and stiffness are distinct concepts in the context of powered joints, and are equivalent in the context of passive joints. The purpose of this paper is to demonstrate the difference between the stiffness and quasi-stiffness using a simple impedance-controlled inverted pendulum model and a more sophisticated biped walking model, each with the ability to modify the trajectory of an impedance controller´s equilibrium angle position. In both cases, stiffness values are specified by the controller and the quasi-stiffness are shown during a single step. Both models have widely varying quasi-stiffness but each have a single stiffness value. Therefore, from this simple modeling approach, the differences and similarities between these two concepts are elucidated.
Keywords :
gait analysis; nonlinear systems; pendulums; physiological models; prosthetics; torque; ankle joint; ankle quasistiffness; ankle stiffness; biomechanical modeling; biped walking model; dynamic tasks; equilibrium angle position trajectory; impedance controlled inverted pendulum model; passive joints; powered prosthetic legs; running; torque-angle relationship; walking mechanical power; Foot; Humans; Impedance; Joints; Legged locomotion; Torque; Trajectory; Ankle impedance; biped model; inverted pendulum; prosthetics; quasi-stiffness; stiffness; Adult; Ankle Joint; Biomechanics; Elasticity; Humans; Male; Models, Biological; Torque; Viscosity; Walking;
fLanguage :
English
Journal_Title :
Biomedical Engineering, IEEE Transactions on
Publisher :
ieee
ISSN :
0018-9294
Type :
jour
DOI :
10.1109/TBME.2012.2230261
Filename :
6365248
Link To Document :
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