Designing Physical Human-Machine-Interfaces for Exoskeletons Using 3D-Shape Analysis

Abstract

Exoskeletons are a promising future technology to assist workers in high demanding workplaces (e.g., activities in or above head level or lifting heavy loads) and to reduce critically strained body parts (e.g., shoulder or back) [1]. Classical exoskeletons generally consist of a mechanical structure parallel to the body segments, actuators for force generation, a control unit (in case of active systems) and human-machine-interfaces (HMI). HMI either fix the exoskeleton to the body or transfer supporting forces from the exoskeleton to the human endoskeleton. At the same time, they need to satisfy safety and comfort requirements [2]. Concerning force transfer too high pressure as well as play within the HMI must be avoided. Precise knowledge of the anthropometric changes in various body positions and muscle states is, therefore, the prerequisite for the design and dimensioning of HMI. This article presents a procedure for designing individual HMI based on 3D shape analysis using the example of activities at head level or above. Based on the general approach [3] the evaluation of the anthropometric changes of upper extremities due to different limb positions and muscle states (relaxed and tensed) is described. Furthermore, the process of data fitting for integrating the individual body parameters into the CAD-construction process is introduced. Three human subjects were integrated into the experimental study, representing different figure types according to ISO 8559-2:2017 [4]. Body postures were scanned using the 3D laser body scanner VITUSbodyscan (Vitronic GmbH), characterizing daily postures of production activities in or above head level as an example for industrial work. In order to compare the scans in relaxed and tensed muscle states as well as in different limb positions with high precision, physical markers and handholds were used. Raw scans were processed and reconstructed with ArthroScan Software tools (Avalution GmbH), 3D shape analysis was calculated for anthropometric changes of the upper arm. In a first step, orthogonal planes to the upper arm were generated and multiplied using Geomagic Freeform to gain intersections with the arm. In the next step, the intersections were fitted into ellipses using Matlab. Finally, the ellipse data formed the basis for the automated CAD-process to create an individual HMI. The results of the study reveal a strong indication that individual human-machine-interfaces are needed to achieve satisfaction concerning fitting, force transfer and safety aspects.

The Influence of Circular Physical Human–Machine Interfaces of Three Shoulder Exoskeletons on Tissue Oxygenation

“…Mean pressure values increased in the dynamic use of the exoskeleton on average for 66%, 69%, and 61% in Lucy, Paexo Shoulder, and Skelex 360, respectively. This increase in pressure is likely attributed to the displacement of the muscle belly during the movement and the change in muscle tone during the experimental task or the relative displacement between exoskeletal and biological interface components [15,55].…”

“…To optimize the pHMI fit, a design approach could be to account for human anthropometric heterogeneity and changes in volume during movement by performing anthropometric studies specifically tailored to the body region of a certain interface with the aid of 3D shape analysis [55,61]. In a second step, it is necessary to ensure that interfaces remain in position, either through active control (active exoskeletons) [62,63] or biomechanical measurements of relative movements (passive exoskeletons) [50].…”