@article {970,
	title = {Energy-Efficient Actuator Design Principles for Robotic Leg Prostheses and Exoskeletons: A Review of Series Elasticity and Backdrivability},
	journal = {ASME Journal of Computational and Nonlinear Dynamics},
	year = {2023},
	abstract = {<p>Robotic leg prostheses and exoskeletons have traditionally been designed using highly-geared motor-transmission systems that minimally exploit the passive dynamics of human locomotion, resulting in inefficient actuators that require significant energy consumption and thus provide limited battery-powered operation or require large onboard batteries. Here we review two of the leading energy-efficient actuator design principles for legged and wearable robotic systems: series elasticity and backdrivability. As shown by inverse dynamic simulations of walking, there are periods of negative joint mechanical work that can be used to increase efficiency by recycling some of the otherwise dissipated energy using series elastic actuators and/or backdriveable actuators with energy regeneration. Series elastic actuators can improve shock tolerance during foot-ground impacts and reduce the peak power and energy consumption of the electric motor via mechanical energy storage and return. However, actuators with series elasticity tend to have lower output torque, increased mass and architecture complexity due to the added physical spring, and limited force and torque control bandwidth. High torque density motors with low-ratio transmissions, known as quasi-direct drives, can likewise achieve low output impedance and high backdrivability, allowing for safe and compliant human-robot physical interactions, in addition to energy regeneration. However, torque-dense motors tend to have higher Joule heating losses, greater motor mass and inertia, and require specialized motor drivers for real-time control. While each actuator design has advantages and drawbacks, designers should consider the energy-efficiency of robotic leg prostheses and exoskeletons beyond steady-state level-ground walking.</p>
},
	keywords = {Actuators, Energy-Efficiency, Exoskeletons, Legged Locomotion, Prosthetics, Wearable Robotics},
	doi = {10.1115/1.4056919},
	url = {https://asmedigitalcollection.asme.org/computationalnonlinear/article-abstract/doi/10.1115/1.4056919/1159612/Energy-Efficient-Actuator-Design-Principles-For?redirectedFrom=fulltext},
	author = {Brokoslaw Laschowski and John McPhee}
}
@inproceedings {959,
	title = {Simulation of Energy Regeneration in Human Locomotion for Efficient Exoskeleton Actuation},
	booktitle = {IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob)},
	year = {2022},
	month = {11/2022},
	publisher = {IEEE},
	organization = {IEEE},
	abstract = {<p>Backdriveable actuators with energy regeneration can improve the efficiency and extend the battery-powered operating times of robotic lower-limb exoskeletons by converting some of the otherwise dissipated energy during negative mechanical work into electrical energy. However, previous related studies have focused on steady-state level-ground walking. To better encompass real-world community mobility, here we developed a feedforward human-exoskeleton energy regeneration system model to simulate energy regeneration and storage during other daily locomotor activities. Data from inverse dynamics analyses of 10 healthy young adults walking at variable speeds and slopes were used to calculate the negative joint mechanical power and work (i.e., the mechanical energy theoretically available for electrical energy regeneration). These human joint mechanical energetics were then used to simulate backdriving a robotic exoskeleton and regenerating energy. An empirical characterization of the exoskeleton device was carried out using a joint dynamometer system and an electromechanical motor model to calculate the actuator efficiency and to simulate energy regeneration. Our performance calculations showed that regenerating energy at slower walking speeds and decline slopes could significantly extend the battery-powered operating times of robotic lower-limb exoskeletons (i.e., up to 99\% increase in total number of steps), therein improving locomotor efficiency.</p>
},
	keywords = {Actuators, Biomechatronics, Energy-Efficiency, Exoskeletons},
	doi = {10.1109/BioRob52689.2022.9925349},
	url = {https://ieeexplore.ieee.org/document/9925349},
	author = {Brokoslaw Laschowski and Keaton A. Inkol and Alex Mihailidis and John McPhee}
}
