Subjective Evaluation of a Passive Lower-Limb Industrial Exoskeleton Used During simulated Assembly

OCCUPATIONAL APPLICATIONS

This study showed an overall positive judgment of users when using a passive lower-limb exoskeleton (Chairless Chair^®, noonee AG, Switzerland), in terms of high levels of comfort and low levels of discomfort. These findings are promising with regard to field implementation, although final steps in the exoskeleton design first have to be taken. In future feasibility studies, users’ acceptance of the exoskeleton should be investigated in the field. One important question that remains is when and for how long users should wear and use the exoskeleton, and areas of beneficial field application need to be defined with regard to primary, secondary, and tertiary prevention, which may provide guidelines for effective use.

TECHNICAL ABSTRACT

Background: Besides efficacy with regard to workload, subjective evaluation (wearing comfort and discomfort, and user acceptance) is an important secondary outcome to determine in field effectiveness studies, before true field implementation of industrial passive and active exoskeletons can be realized. Purpose: The aim of this study was to determine how discomfort and wearer comfort change with the use of a passive lower-limb exoskeleton and how both are influenced by optimal and suboptimal working heights. Methods: Forty-five male participants were included in the study. Each performed a simulated assembly task in seven experimental conditions, which were a combination of working posture (standing without the exoskeleton, and high and low sitting on the exoskeleton) and working height (optimal and suboptimal). The simulated task included screwing, clip fitting, and cable mounting, and was performed for 21 min in each condition. Before and after each condition, participants rated their level of discomfort, and after completed all conditions they provided feedback about comfort. Results: Initial discomfort ratings (i.e., before each condition) were all < 2 (on a 0–10 scale), with a mean initial rating of 0.03 (SD 0.22). Overall increases in discomfort levels across conditions remained below 1.4, but were significantly lower in the standing working posture without the exoskeleton. Wearer comfort was rated high, with a general mean rating of 7.9 (on a 1–10 scale). Wearer comfort was rated slightly higher for the low versus the high sitting configuration on the exoskeleton. Conclusions: These subjective assessments of discomfort and wearer comfort suggest that the Chairless Chair^® has the potential to be used in the occupational context. Future work is recommended, though, include field testing to evaluate user acceptability of the exoskeleton as well as a thorough evaluation of work situations wherein workers can benefit from the use of the exoskeleton.

Keywords:

• manual materials handling
• industry
• ergonomics
• lower extremity
• standing work
• numeric rating scale

ACKNOWLEDGMENTS

The authors would like to thank Theresa J. Kreidler for her help during the measurement preparations and data collection and Martina Michaelis for her feedback on the evaluation questionnaire. We would also like to thank AUDI AG for their financial contribution to this study, for providing us two exoskeletons, and for their input in developing the study design.

CONFLICT OF INTEREST

The authors declare no conflict of interest.