Achilles: An autonomous lightweight ankle exoskeleton to provide push-off power

This paper presents the Achilles exoskeleton, an autonomous ankle exoskeleton that can generate 52% of the positive plantarflexion power around the ankle of a 80 kg individual with only 1.5 kg of mass added around the ankle joint. The mass of the exoskeleton is lower and the power density is higher than that of existing autonomous exoskeletons. This high power density was achieved by designing a series elastic actuator that consists of an electric motor and ball-screw gear with a carbon fiber reinforced leaf-spring as lever-arm. A dynamic model that includes the motor and gear properties, spring stiffness, and exoskeleton geometry was used to optimize the design parameters for positive power injection. Doing this for multiple combinations of preselected motors and gears and comparing their support to weight ratio, revealed the best drive combination. The performance of the realized exoskeleton was assessed in several tests. The actuator can track the optimized actuator stroke trajectory with a following error that has a RMS of 2.3 mm, it can track force reference signals with amplitudes of 1 N to 100 N with a bandwidth between 8.1 Hz and 20.6 Hz, and it outputs a maximum mechanical power of 80.2 W. These results show that the device is suitable for fulfilling its purpose: reducing the metabolic cost of walking with an autonomous device.

[1]  David A. Winter,et al.  Biomechanics and Motor Control of Human Movement , 1990 .

[2]  J. Donelan,et al.  Mechanical work for step-to-step transitions is a major determinant of the metabolic cost of human walking. , 2002, The Journal of experimental biology.

[3]  Jerry E. Pratt,et al.  The RoboKnee: an exoskeleton for enhancing strength and endurance during walking , 2004, IEEE International Conference on Robotics and Automation, 2004. Proceedings. ICRA '04. 2004.

[4]  H. Herr,et al.  Adaptive control of a variable-impedance ankle-foot orthosis to assist drop-foot gait , 2004, IEEE Transactions on Neural Systems and Rehabilitation Engineering.

[5]  P. Komi,et al.  Muscle-tendon interaction and elastic energy usage in human walking. , 2005, Journal of applied physiology.

[6]  Andy Ruina,et al.  Energetic Consequences of Walking Like an Inverted Pendulum: Step-to-Step Transitions , 2005, Exercise and sport sciences reviews.

[7]  Robert Ilg,et al.  An efficient robotic tendon for gait assistance. , 2006, Journal of biomechanical engineering.

[8]  James A. Norris,et al.  Effect of augmented plantarflexion power on preferred walking speed and economy in young and older adults. , 2007, Gait & posture.

[9]  Thomas Sugar,et al.  Dynamically Controlled Ankle-Foot Orthosis (DCO) with Regenerative Kinetics: Incrementally Attaining User Portability , 2007, Proceedings 2007 IEEE International Conference on Robotics and Automation.

[10]  Monica A. Daley,et al.  A Physiologist's Perspective on Robotic Exoskeletons for Human Locomotion , 2007, Int. J. Humanoid Robotics.

[11]  R. Kram,et al.  The effects of adding mass to the legs on the energetics and biomechanics of walking. , 2007, Medicine and science in sports and exercise.

[12]  Martin Buss,et al.  Compliant actuation of rehabilitation robots , 2008, IEEE Robotics & Automation Magazine.

[13]  Daniel P. Ferris,et al.  Mechanics and energetics of level walking with powered ankle exoskeletons , 2008, Journal of Experimental Biology.

[14]  Yasushi Ikeuchi,et al.  Walking assist device with bodyweight support system , 2009, 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems.

[15]  Daniel P Ferris,et al.  Invariant ankle moment patterns when walking with and without a robotic ankle exoskeleton. , 2010, Journal of biomechanics.

[16]  Herman van der Kooij,et al.  The effect of directional inertias added to pelvis and ankle on gait , 2013, Journal of NeuroEngineering and Rehabilitation.

[17]  D. De Clercq,et al.  A Simple Exoskeleton That Assists Plantarflexion Can Reduce the Metabolic Cost of Human Walking , 2013, PloS one.

[18]  Herman van der Kooij,et al.  Modeling, design, and optimization of Mindwalker series elastic joint , 2013, 2013 IEEE 13th International Conference on Rehabilitation Robotics (ICORR).