Robust Optimal Design of Energy Efficient Series Elastic Actuators: Application to a Powered Prosthetic Ankle

Design of rehabilitation and physical assistance robots that work safely and efficiently despite uncertain operational conditions remains an important challenge. Current methods for the design of energy efficient series elastic actuators use an optimization formulation that typically assumes known o...

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Bibliographic Details
Published in:2019 IEEE 16th International Conference on Rehabilitation Robotics (ICORR) 2019-06, Vol.2019, p.740-747
Main Authors: Bolivar, Edgar, Rezazadeh, Siavash, Summers, Tyler, Gregg, Robert D.
Format: Article
Language:English
Subjects:
Actuators
Ankle Joint - physiology
Computer Simulation
DC motors
Elasticity
Energy consumption
Equipment Design
Humans
Joint Prosthesis
Motor Activity
Robotics - instrumentation
Springs
Torque
Trajectory
Uncertainty
Walking - physiology
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Summary:Design of rehabilitation and physical assistance robots that work safely and efficiently despite uncertain operational conditions remains an important challenge. Current methods for the design of energy efficient series elastic actuators use an optimization formulation that typically assumes known operational requirements. This approach could lead to actuators that cannot satisfy elongation, speed, or torque requirements when the operation deviates from nominal conditions. Addressing this gap, we propose a convex optimization formulation to design the stiffness of series elastic actuators to minimize energy consumption and satisfy actuator constraints despite uncertainty due to manufacturing of the spring, unmodeled dynamics, efficiency of the transmission, and the kinematics and kinetics of the load. To achieve convexity, we write energy consumption as a scalar convex-quadratic function of compliance. As actuator constraints, we consider peak motor torque, peak motor velocity, limitations due to the speed-torque relationship of DC motors, and peak elongation of the spring. We apply our formulation to the robust design of a series elastic actuator for a powered prosthetic ankle. Our simulation results indicate that a small trade-off between energy efficiency and robustness is justified to design actuators that can operate with uncertainty.
ISSN:1945-7898
1945-7901
DOI:10.1109/ICORR.2019.8779446