Category: News

The paper is entitled “The value of time in the invigoration of human movements when interacting with a robotic exoskeleton“, and available in open-access here:

https://www.science.org/doi/full/10.1126/sciadv.adh9533

by Dorian Verdel, Olivier Bruneau, Guillaume Sahm, Nicolas Vignais, and Bastien Berret

Abstract

Time and effort are critical factors that are thought to be subjectively balanced during the planning of goal-directed actions, thereby setting the vigor of volitional movements. Theoretical models predicted that the value of time should then amount to relatively high levels of effort. However, the time-effort tradeoff has so far only been studied for a narrow range of efforts. Therefore, the extent to which humans can invest in a time-saving effort remains largely unknown. To address this issue, we used a robotic exoskeleton which significantly varied the energetic cost associated with a certain vigor during reaching movements. In this situation, minimizing the time-effort tradeoff would lead to high and low human efforts for upward and downward movements respectively. Consistent with this prediction, results showed that all participants expended substantial amounts of energy to pull on the exoskeleton during upward movements and remained essentially inactive by harnessing the work of gravity to push on the exoskeleton during downward movements, while saving time in both cases. These findings show that a common tradeoff between time and effort can determine the vigor of reaching movements for a wide range of efforts, with time cost playing a pivotal role.

The paper is entitled “Human Exteroception during Object Handling with an Upper Limb Exoskeleton“, and available in open-access here:

https://www.mdpi.com/1424-8220/23/11/5158

by Dorine Arcangeli, Océane Dubois, Agnès Roby-Brami, Sylvain Famié, Giovanni de Marco, Gabriel Arnold, Nathanaël Jarrassé and Ross Parry

Abstract

Upper limb exoskeletons may confer significant mechanical advantages across a range of tasks. The potential consequences of the exoskeleton upon the user’s sensorimotor capacities however, remain poorly understood. The purpose of this study was to examine how the physical coupling of the user’s arm to an upper limb exoskeleton influenced the perception of handheld objects. In the experimental protocol, participants were required to estimate the length of a series of bars held in their dominant right hand, in the absence of visual feedback. Their performance in conditions with an exoskeleton fixed to the forearm and upper arm was compared to conditions without the upper limb exoskeleton. Experiment 1 was designed to verify the effects of attaching an exoskeleton to the upper limb, with object handling limited to rotations of the wrist only. Experiment 2 was designed to verify the effects of the structure, and its mass, with combined movements of the wrist, elbow, and shoulder. Statistical analysis indicated that movements performed with the exoskeleton did not significantly affect perception of the handheld object in experiment 1 (BF₀₁ = 2.3) or experiment 2 (BF₀₁ = 4.3). These findings suggest that while the integration of an exoskeleton complexifies the architecture of the upper limb effector, this does not necessarily impede transmission of the mechanical information required for human exteroception.

The paper is entitled “A Trade-Off between Complexity and Interaction Quality for Upper Limb Exoskeleton Interfaces“, and available in open-access here:

https://www.mdpi.com/1424-8220/23/8/4122

by Dorian Verdel, Guillaume Sahm, Olivier Bruneau, Bastien Berret and Nicolas Vignais

Abstract

Exoskeletons are among the most promising devices dedicated to assisting human movement during reeducation protocols and preventing musculoskeletal disorders at work. However, their potential is currently limited, partially because of a fundamental contradiction impacting their design. Indeed, increasing the interaction quality often requires the inclusion of passive degrees of freedom in the design of human-exoskeleton interfaces, which increases the exoskeleton’s inertia and complexity. Thus, its control also becomes more complex, and unwanted interaction efforts can become important. In the present paper, we investigate the influence of two passive rotations in the forearm interface on sagittal plane reaching movements while keeping the arm interface unchanged (i.e., without passive degrees of freedom). Such a proposal represents a possible compromise between conflicting design constraints. The in-depth investigations carried out here in terms of interaction efforts, kinematics, electromyographic signals, and subjective feedback of participants all underscored the benefits of such a design. Therefore, the proposed compromise appears to be suitable for rehabilitation sessions, specific tasks at work, and future investigations into human movement using exoskeletons.

Verdel, D., Sahm, G., Bastide, S., Bruneau, O., Berret, B., & Vignais, N. (2022) Influence of the physical interface on the quality of human-exoskeleton interaction. IEEE Transactions on Human-Machine Systems, [link]

Abstract: Despite exoskeletons becoming widespread tools in
industrial applications, the impact of the design of humanexoskeleton
physical interfaces has received little attention. The
present study aims at thoroughly quantifying the influence of
different physical human-exoskeleton interfaces on subjective and
objective biomechanical parameters. To this aim, 18 participants
performed elbow flexion/extension movements while wearing an
active exoskeleton with three different physical interfaces: a strap
without any degree of freedom, a thermoformed orthosis with
one (translation) and three degrees of freedom (translation and
rotations). Interaction efforts, kinematic parameters, electromyographic
activities and subjective feelings were collected and
examined during the experiment. Results showed that increasing
the interaction area is necessary to improve the interaction
quality at a subjective level. The addition of passive degrees
of freedom allows significant improvements on both subjective
and objective measurements. Outcomes of the present study may
provide fundamental insights to select physical interfaces when
designing future exoskeletons.

Verdel, D., Bastide, S., Vignais, N., Bruneau, O., & Berret, B. (2022). Human Weight Compensation With a Backdrivable Upper-Limb Exoskeleton: Identification and Control. In Frontiers in Bioengineering and Biotechnology (Vol. 9). [link]

Two papers from conference proceedings have been accepted for publication and communication.

• Verdel, D., Bastide, S., Bruneau, O., Berret, B., Vignais, N. Improving and quantifying the transparency of an upper-limb robotic exoskeleton with a force sensor and electromyographic measures. Computer Methods in Biomechanics and Biomedical Engineering, accepted. Paper considered for publication after the French Society of Biomechanics. Saint-Etienne, France, 25-27 of Oct., 2021.
• Vignais, N., Verdel, D., Bastide, S., Bruneau, O., Berret B. An identification method to improve the transparency of an exoskeleton: development and validation. Proceedings of the Association des Chercheurs en Activités Physiques et Sportives (ACAPS), Montpellier, France, 2021.

N. Vignais and D. Verdel will present these results during the conferences.