title: Spring uses in exoskeleton actuation design.
abstract: An exoskeleton has to be lightweight, compliant, yet powerful to fulfill the demanding task of walking. This imposes a great challenge for the actuator design. Electric motors, by far the most common actuator in robotic, orthotic, and prosthetic devices, cannot provide sufficiently high peak and average power and force/torque output, and they normally require high-ratio, heavy reducer to produce the speeds and high torques needed for human locomotion. Studies on the human muscle-tendon system have shown that muscles (including tendons and ligaments) function as a spring, and by storing energy and releasing it at a proper moment, locomotion becomes more energy efficient. Inspired by the muscle behavior, we propose a novel actuation strategy for exoskeleton design. In this paper, the collected gait data are analyzed to identify the spring property of the human muscle-tendon system. Theoretical optimization results show that adding parallel springs can reduce the peak torque by 66%, 53%, and 48% for hip flexion/extension (F/E), hip abduction/adduction (A/A), and ankle dorsi/plantar flexion (D/PF), respectively, and the rms power by 50%, 45%, and 61%, respectively. Adding a series spring (forming a Series Elastic Actuator, SEA) reduces the peak power by 79% for ankle D/PF, and by 60% for hip A/A. A SEA does not reduce the peak power demand at other joints. The optimization approach can be used for designing other wearable robots as well.
authors.affiliation: Biomechanical Engineering Dept., Delft University of Technology (TU Delft), Delft, The Netherlands. shiqian.wang@tudelft.nl
authors.forename: Shiqian
authors.initials: S
authors.lastname: Wang
authors.forename: Wietse
authors.initials: W
authors.lastname: van Dijk
authors.forename: Herman
authors.initials: H
authors.lastname: van der Kooij
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D005260:Female; D005684:Gait / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D009989:Orthotic Devices; D012371:Robotics / Q000295:instrumentation / Q000379:methods*; D013119:Spinal Cord Injuries / Q000534:rehabilitation; D016138:Walking / Q000502:physiology*; D055815:Young Adult