Title: A comparison of different methods for modelling the physical human-exoskeleton interface

Authors: Divyaksh Subhash Chander; Max Böhme; Michael Skipper Andersen; John Rasmussen; Johannes Zentner; Maria Pia Cavatorta

Addresses: Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Corso Duca Degli Abruzzi, 24, 10129 Torino, Italy ' Faculty of Engineering, Leipzig University of Applied Sciences, Karl-Liebknecht-Str. 132, 04277 Leipzig, Germany; Faculty V – Mechanical Engineering and Transport Systems, Technical University Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany ' Department of Materials and Production, Aalborg University, Fibigerstræde 16, 9220 Aalborg Ø., Denmark ' Department of Materials and Production, Aalborg University, Fibigerstræde 16, 9220 Aalborg Ø., Denmark ' Faculty of Engineering, Leipzig University of Applied Sciences, Karl-Liebknecht-Str. 132, 04277 Leipzig, Germany ' Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Corso Duca Degli Abruzzi, 24, 10129 Torino, Italy

Abstract: There are several methods to simulate the human-exoskeleton interface but there is insufficient evidence regarding the choice of the method. This work compares two rigid-body methods to simulate the interface: 1) optimisation-based contact forces; 2) reaction forces at a point on the interface. Additionally, a method to kinetically align the human-exoskeleton joint axes is presented. A single subject tested an active lower limb exoskeleton in stair ascent. The biomechanical outputs were compared to a baseline model, where the measured assistive and ground reaction forces were applied directly to the human model. Both methods showed negligible differences in knee compression force, knee flexion moment, and vastus lateralis activation. However, the ankle outputs showed some differences between the methods. Computationally expensive contact forces provided six-axis interface forces unlike reaction forces, which were limited to the number of constraints required by the exoskeleton. Future studies could compare rigid-body and viscoelastic models.

Keywords: human-exoskeleton interface; interaction force; joint misalignment; musculoskeletal model; contact model; contact force.

DOI: 10.1504/IJHFMS.2022.124310

International Journal of Human Factors Modelling and Simulation, 2022 Vol.7 No.3/4, pp.204 - 230

Received: 21 Oct 2021
Received in revised form: 08 Mar 2022
Accepted: 21 Apr 2022
Published online: 21 Jul 2022 *