Physical interface dynamics alter how robotic exosuits augment human movement: implications for optimizing wearable assistive devices

Your doctor can explain how this news impacts the exosuits that are being used in their stroke department. Ask if soft exosuits have different effects.

Physical interface dynamics alter how robotic exosuits augment human movement: implications for optimizing wearable assistive devices

• Matthew B. YandellEmail author,
• Brendan T. Quinlivan,
• Dmitry Popov,
• Conor Walsh and
• Karl E. Zelik

Journal of NeuroEngineering and Rehabilitation201714:40

DOI: 10.1186/s12984-017-0247-9

©  The Author(s). 2017

Received: 11 February 2017

Accepted: 21 April 2017

Published: 18 May 2017

Abstract

Background

Wearable assistive devices have demonstrated the potential to improve mobility outcomes for individuals with disabilities, and to augment healthy human performance; however, these benefits depend on how effectively power is transmitted from the device to the human user. Quantifying and understanding this power transmission is challenging due to complex human-device interface dynamics that occur as biological tissues and physical interface materials deform and displace under load, absorbing and returning power.

Methods

Here we introduce a new methodology for quickly estimating interface power dynamics during movement tasks using common motion capture and force measurements, and then apply this method to quantify how a soft robotic ankle exosuit interacts with and transfers power to the human body during walking. We partition exosuit end-effector power (i.e., power output from the device) into power that augments ankle plantarflexion (termed augmentation power) vs. power that goes into deformation and motion of interface materials and underlying soft tissues (termed interface power).

Results

We provide empirical evidence of how human-exosuit interfaces absorb and return energy, reshaping exosuit-to-human power flow and resulting in three key consequences: (i) During exosuit loading (as applied forces increased), about 55% of exosuit end-effector power was absorbed into the interfaces. (ii) However, during subsequent exosuit unloading (as applied forces decreased) most of the absorbed interface power was returned viscoelastically. Consequently, the majority (about 75%) of exosuit end-effector work over each stride contributed to augmenting ankle plantarflexion. (iii) Ankle augmentation power (and work) was delayed relative to exosuit end-effector power, due to these interface energy absorption and return dynamics.