Evaluation of Active Shoulder Exoskeleton Support to Deduce Application-Oriented Optimization Potentials for Overhead Work

Abstract

Repetitive overhead work with a heavy load increases the risk for work-related shoulder disorders. Occupational exoskeletons supporting arm elevation are potential solutions to reduce that risk by lowering the physical strains on the shoulder. Many studies have reported a reduction in shoulder stress in various overhead tasks by using such exoskeletons. However, the support demand can vary in each phase of motion as well as in each individual task. This paper presents a laboratory study with five participants to evaluate the influence of the support level of an active shoulder exoskeleton in different motion phases (e.g., arm lifting, screw-in, and arm lowering of two overhead tasks) to identify the potential optimization of support at each phase. Results show that the support level of the exoskeleton should be adapted to the motion phase of the two chosen tasks. A higher support force is desired for the screw phase compared to the arm lifting and lowering phases, and the support level needs to be reduced immediately for arm lowering after the screw phase. The time for switching the support levels can be recognized by the electric current of the screwdriver.

A Novel Approach to Simulating Realistic Exoskeleton Behavior in Response to Human Motion

“…Its upper extremities are modeled by Holzbaur et al [26] with 15 degrees of freedom for the shoulder, elbow, forearm, wrist, thumb, and index finger. The kinetic simulation of the DHM is based on the motions recorded by a motion capture system (Vicon Bonita, Oxford Metrics Ltd., Oxford, UK) during a previous lab study [27]. The marker placement follows the Vicon guide for the full-body model [28].…”

“…Two groups of simulations are conducted, summarized in Table 1, for the validation of the human-motion-based simulation approach. Motion data of three participants (P1-P3) from the previous lab study of the exoskeleton Lucy [27] are used as input for the simulations. In the lab study, two overhead tasks (T1 and T2) with a screwdriver are defined.…”

A Co-Simulation Model Integrating a Musculoskeletal Human Model with Exoskeleton and Power Tool Model

“…The interface between the human and the power tool is defined by a reference point located on the palm of the dominant hand of the user. The power tool model determines the load (forces and torques on the human) at this reference point using experimental data from the study described by Sänger et al [43] as input for the interaction simulation. The model integrates the motion data recorded by the Vicon motion capture system, the ground reaction forces (GRF), and the battery current of the cordless screwdriver.…”

“…The model integrates the motion data recorded by the Vicon motion capture system, the ground reaction forces (GRF), and the battery current of the cordless screwdriver. The user's applied push force is calculated from the GRF, while the screwdriver´s battery current is used to estimate the process torque applied to the screwdriver during the screw-in process using the correlation model [43].…”

“…Here, one hand was used to position the predrilled wooden component (non-dominant hand), while the other hand uses the cordless screwdriver to screw (dominant hand). The use case is shown in Figure 7 and the study is described in detail by Sänger et al [43]. For the evaluation of the co-simulation model, the data of three subjects (age: 24 ± 3.6 years, weight: 74.4 ± 16.1 kg, height: 1.84 ± 0.03 m, sex: male) were used.…”