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Design and Evaluation of a Quasi-Passive Knee Exoskeleton for Investigation of Motor Adaptation in Lower Extremity Joints

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Kamran Shamaei, Massimo Cenciarini, Albert A. Adams, Karen N. Gregorczyk, Jeffrey M. Schiffman, and Aaron M. Dollar, Yale University, Neurologische Universitätsklinik Freiburg, and US Army Natick Soldier Research, Development and Engineering Center, Natick,  Volume 61, Issue 6, Page: 1809-1821

July Shamael Image-01-1

Lower-extremity exoskeletons have been actively investigated in the past few decades intending to augment the locomotion performance of able-bodied users in terms of metabolic cost, load carrying capacity, fatigue, and muscle force generation. While development efforts have been extensive, lower-limb exoskeleton devices have demonstrated limited success in achieving their augmentation goals, highlighting the challenges in developing artificial systems that can augment the performance of the human body, which is generally substantially more efficient than engineered systems. In this paper, we describe the mechanical design and control scheme of a quasi-passive knee exoskeleton intended to investigate the biomechanical behavior of the knee joint during interaction with externally-applied impedances. As the human knee behaves much like a linear spring during the stance phase of normal walking gait, the exoskeleton implements a spring across the knee in the weight acceptance phase of the gait while allowing free motion throughout the rest of the gait cycle, accomplished via an electromechanical clutch. We describe a preliminary experiment on three healthy adults to evaluate the functionality of the device on both left and right legs. The kinetic and kinematic analyses of these subjects show that the exoskeleton assistance can partially/fully replace the function of the knee joint because moment and angle profiles for the hip and ankle joints as well as the overall knee joint and exoskeleton complex were found nearly invariant under the externally-applied moments of the exoskeleton versus the control condition. This finding suggests that the subjects undergo a considerable amount of motor adaptation in their lower extremities to the exoskeletal impedances.

Keywords: Lower extremity exoskeleton, variable-stiffness, knee biomechanics, quasi-passive mechanism, orthosis, prosthesis

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