Design and Sensor Based Evaluation of Custom-Fit Coupling Interfaces for Lower Limb Exoskeletons: A Pilot Study

The coupling interface on wearable lower limb exoskeletons influence physical human-robot interactions (pHRI) that occur during assistance in gait and posture tasks. Despite their increasing popularity, risks to the user (i.e., skin, musculoskeletal injuries) from undesirable interactions at the interface are present. Current research examining coupling interactions, focuses on characterizing simple pressure measures (i.e., mean) independent of interface features. Consequently, design guidelines of ideal coupling interface interactions do not yet exist due to a lack of common framework and metrics tied to interface features for analysis. Other wearable devices (e.g. prostheses), use custom fit interfaces as a baseline for interface design. In this study we compare custom made single-user and generic multi-user interfaces using established and novel pressure-related measures. 5 minute overground gait trials were conducted with pressure sensors placed at the hip and thigh interfaces. Pilot study results showed increased supporting contact area at the measured surfaces and a reduction in relative movement during use of custom-fit interfaces. Average and peak pressure varied between sites, with custom thigh interfaces exhibiting notable improved performance. Pressure measures reported highlight the benefit of custom interfaces, and the value of additional pressure analysis metrics in differentiating interface designs and evaluating relative performance. We propose that custom fit interfaces can provide a common baseline for evaluating coupling interface pHRI, supported by novel methods of pressure analysis to tie pHRI improvements to specific interface design characteristics.