posted on 2018-07-13, 08:24authored byStefano Toxiri, Axel S. Koopman, Maria Lazzaroni, Jesús Ortiz, Valerie Power, Michiel P. de Looze, Leonard O'SullivanLeonard O'Sullivan, Darwin G. Caldwell
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.
Funding
Study on Aerodynamic Characteristics Control of Slender Body Using Active Flow Control Technique