Novel method for setting population-specific joint torque assistance requirements with applications to exoskeleton design

Abstract

This paper presents a novel methodology to calculate assistance requirements for wearable robotic devices (e.g., exoskeletons) using Maximum Voluntary Contraction (MVC) measurements. While other methods for determining assistance requirements focus on the kinematics and kinetics of specific tasks to be performed, our method determines the assistance needed for a population to reach the overall physical capabilities of another reference population. While applicable to any joint and population, we demonstrate its effectiveness on the lower limb joints of older adults. Unlike conventional methods that assume the need to provide 100% of the peak torque during the assisted task, our approach calculates the required assistance and identifies a 2 0 – 2 5% torque deficit for setting assistive torque requirements. This discrepancy underscores the importance of addressing the physical deficits of its users when designing assistive devices. As our method provides torque deficit as a function of joint velocity, the characteristics of the actuator can be chosen to match these deficits. Additionally, as the torque deficit is described as a function of joint angle, non-linear transmissions can be designed in future actuation systems of assistive wearable devices.