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Front. Robot. AI | doi: 10.3389/frobt.2018.00053

Rationale, Implementation and Evaluation of Assistive Strategies for an Active Back-Support Exoskeleton

  • 1Fondazione Istituto Italiano di Technologia, Italy
  • 2Department of Human Movement Sciences, Library Vrije Universiteit Amsterdam, Netherlands
  • 3School of Design, Health Research Institute, University of Limerick, Ireland

Active exoskeletons are potentially more effective and versatile than passive ones, but designing them poses a number of additional challenges. An important open challenge in the field is associated to the assistive strategy, by which the actuation forces are modulated to the user’s needs during the physical activity. This paper addresses this challenge on an active exoskeleton prototype aimed at reducing compressive low-back loads, associated to risk of musculoskeletal injury during manual material handling (i.e. repeatedly lifting objects).
An analysis of the biomechanics of the physical task reveals two key factors that determine low- back loads. For each factor, a suitable control strategy for the exoskeleton is implemented. The first strategy is based on user posture and modulates the assistance to support the wearer’s own upper body. The second one adapts to the mass of the lifted object and is a practical implementation of electromyographic control. A third strategy is devised as a generalized combination of the first two. With these strategies, the proposed exoskeleton can quickly adjust to different task conditions (which makes it versatile compared to using multiple, task-specific, devices) as well as to individual preference (which promotes user acceptance). Additionally, the presented implementation is potentially applicable to more powerful exoskeletons, capable of generating larger forces.
The different strategies are implemented on the exoskeleton and tested on 11 participants in an experiment reproducing the lifting task. The resulting data highlights that the strategies modulate the assistance as intended by design, i.e. they effectively adjust the commanded assistive torque during operation based on user posture and external mass. The experiment also provides evidence of significant reduction in muscular activity at the lumbar spine (around 30%) associated to using the exoskeleton. The reduction is well in line with previous literature and may be associated to lower risk of injury.

Keywords: exoskeleton, Powered, Back support, manual handling, strategy, Myocontrol, Electromyography

Received: 15 Jan 2018; Accepted: 16 Apr 2018.

Edited by:

Simona Crea, Scuola Sant'Anna di Studi Avanzati, Italy

Reviewed by:

Yan Tingfang, The Chinese University of Hong Kong, China
Enhao Zheng, Institute of Automation (CAS), China  

Copyright: © 2018 Toxiri, Koopman, Lazzaroni, Ortiz, Power, de Looze, O'Sullivan and Caldwell. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mr. Stefano Toxiri, Fondazione Istituto Italiano di Technologia, Genoa, Italy, stefano.toxiri@iit.it