Force Transfer Characterization of a Soft Exosuit for Gait Assistance

Abstract

Recently, there has been a growing interest in moving away from traditional rigid exoskeletons towards soft exosuits that can provide a variety of advantages including a reduction in both the weight carried by the wearer and the inertia experienced as the wearer flexes and extends their joints. These advantages are achieved by using structured functional textiles in combination with a flexible actuation scheme that enables assistive torques to be applied to the biological joints. Understanding the human-suit interface in these systems is important, as one of the key challenges with this approach is applying force to the human body in a manner that is safe, comfortable, and effective. This paper outlines a methodology for characterizing the structured functional textile of soft exosuits and then uses that methodology to evaluate several factors that lead to different suit-human series stiffnesses and pressure distributions over the body. These factors include the size of the force distribution area and the composition of the structured functional textile. Following the test results, design guidelines are suggested to maximize the safety, comfort, and efficiency of the exosuit.

Development and validation of a soft robotic exosuit for assistance of the upper limbs

“…Gear train Quinlivan and colleagues proposed a method for assessing the stiffness of the exosuit and of the underlying human tissue [67]. The procedure consists in assuming the compliance between the motor and the user's skeletal structure can be modelled as two linear elastic elements in series ( Figure 3.8.b), one given by the suit k s , i.e.…”

“…The big mismatch between P elbow and P motor highlights the low efficiency of the device, an average over repetitions and subjects just below 20%. Quinlivan et al [67] shows an elegant procedure to choose the best garments and orientation of the fabric fibers to increase stiffness. The authors also suggest to try to load bony prominents of the human body and pre-compress soft tissues, to reduce compliance of the human-suit interface.…”

“…This configuration closely resembles the working principle of Series Elastic Actuators (SEAs). (c) Suit's (red) and human+suit's (blue) stiffness, measured using the methodology describe in[67].…”

“…c shows a characterization of the exosuit's stiffness on a rigid mannequin (red) and on a subject (blue), using the methodology described in[67]. The stiffness can be derived by commanding the suit's motor to apply a linearly increasing forceform 0 N to 100 N (mannequin) and 50 N (human) and back, on the flexing and extending tendons of the suit, and measuring its displacement with the encoder on the motor's axis.…”

“…De Rossi et al proposed an apparatus to monitor the distribution of pressure at the human-robot interface of a lowerlimb exoskeleton during gait training[78]. Using a similar approach, Levesque et al identified areas exhibiting peaks of pressure on the attachment points of an active orthosis for gait assistance[79]; their findings suggest that the distribution of pressure is affected more by the stiffness of the padding material than by its thickness.This data-driven approach to guide design choices is a promising path: Quinlivan et al used the same paradigm to optimise the topology and material composition of the attachment points of a soft exosuit for the lower limbs[67]. This work highlighted the importance of the geometry of the interface (larger areas lead to higher comfort) as well as advising the use of fabric materials that better conform to the human body.Being for exoskeletons or exosuits, materials such as neoprene or polyethilene (PE) sponge are common choices for cushioning the human-robot interface, yet there is no data-supported knowledge to justify the choice of one over others.…”