User-centered evaluation of the Wearable Walker lower limb exoskeleton, preliminary assessment based on the Experience protocol

TL;DR

This study applies the EUROBENCH EXPERIENCE benchmarking framework to a Wearable Walker lower-limb exoskeleton, aiming for a rigorous, replicable evaluation of user experience and physiological impact. The Wearable Walker features a three-layer control stack with a novel Blend Control that interpolates between two single-stance models to provide seamless assistance, validated via a 5-subject EXPERIENCE protocol measuring psychophysiological indicators and a multifactor questionnaire. Results indicate the device does not elevate seated stress and yields generally positive usability metrics, though improvements—especially ankle actuation—are needed to enhance gait assistance and balance. The work demonstrates a practical, standardized pathway for benchmarking wearable robotics and identifies concrete directions for device optimization and broader adoption.

Abstract

Using lower-limbs exoskeletons provides potential advantages in terms of productivity and safety associated with reduced stress. However, complex issues in human-robot interaction are still open, such as the physiological effects of exoskeletons and the impact on the user's subjective experience. In this work, an innovative exoskeleton, the Wearable Walker, is assessed using the EXPERIENCE benchmarking protocol from the EUROBENCH project. The Wearable Walker is a lower-limb exoskeleton that enhances human abilities, such as carrying loads. The device uses a unique control approach called Blend Control that provides smooth assistance torques. It operates two models simultaneously, one in the case in which the left foot is grounded and another for the grounded right foot. These models generate assistive torques combined to provide continuous and smooth overall assistance, preventing any abrupt changes in torque due to model switching. The EXPERIENCE protocol consists of walking on flat ground while gathering physiological signals such as heart rate, its variability, respiration rate, and galvanic skin response and completing a questionnaire. The test was performed with five healthy subjects. The scope of the present study is twofold: to evaluate the specific exoskeleton and its current control system to gain insight into possible improvements and to present a case study for a formal and replicable benchmarking of wearable robots.

Figures (5)

• Figure S1: The Wearable Walker Lower Limb Exoskeleton along with the sensing devices used for the experiment. The CAD models show the kinematic variables and the detail of the two Degrees of Freedom that the thigh harness has with regards to the exoskeleton's thigh link.
• Figure S2: Electronics, computing units and assistance computation architecture of the Wearable Walker Lower Limb Exoskeleton. In the bottom right scheme, red blocks highlights the components of assistive torques reported in Equation \ref{['eq:taus']}
• Figure S3: Scores of the psychophysiological performance indicators (PIs) of the EXPERIENCE protocol for each volunteer. Each point on the X axis represents an average of a 1 minute recording. Curves show the evolution in time of such PIs.
• Figure S4: Scores of the physiological PI of the EXPERIENCE protocol for each volunteer as a function of time. The three protocol phases, i.e. sit, sit exo, and walking are plotted together and marked in the figures.
• Figure S5: Distribution of answers to the questionnaire items. Bars report the average score and the whiskers their standard deviation.