A Sensitivity Analysis of an Economic Value Metric for Quantifying the Success of Lower-Limb Exoskeletons and Their Assistance

Abstract

Modern exoskeletons are typically developed to optimize for a single, physiological objective, the “gold standard” of which is a reduction of the wearer's metabolic rate. However, recent research suggests that these changes in metabolic rate are not yet perceivable on average. To address this gap, this study explores a novel economic value metric to quantify the value of exoskeleton assistance. The overarching goal of this work is the development of a perceptible metric that leverages the user experience to quantify exoskeleton success. We use the Vickrey second-price auction to obtain the monetary compensation needed for participants to continue walking for consecutive two-minute bouts. Comparing the participant's bidding trends when wearing and not wearing an exoskeleton captures the economic value of the experience, termed Marginal Value (MV). To reduce the logistical burden of the auction, we simulated human participants (robo-bidders) to compete alongside real participants. This work presents a sensitivity analysis to understand how the number and bidding behavior of the robo-bidders affects our economic value metric, MV. We found that MV was not significantly affected by the number of robo-bidders or their bidding behavior (i.e. effort rate). The bidding behavior of the human participants was affected by the robo-bidder effort rate, indicating that there is interplay in the bidding dynamics among the auction participants, but these changes do not significantly affect the marginal value. This study tentatively validates the current approach in generating our proposed metric for exoskeleton success, paving the way for economic value to be further explored as a holistic, personalized metric for the development of lower-limb exoskeletons.