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Section: New Results

VR and Ergonomics

Participants : Charles Pontonnier [contact] , Georges Dumont, Franck Multon, Pierre Plantard.

The use of virtual reality tools for ergonomics applications is a very important challenge in order to genezalize the use of such devices for the design of workstations.

First, the development of motion analysis tools is mandatory in order to provide additional information to the ergonomists and help them to analyse the work environment. Particularly, an analysis of the muscle forces involved in the motion generation is a very important information with regard to the ergonomics of a task. Several methods can lead to an estimation of these muscle forces. In a study we developed, we tried to assess the level of confidence for results obtained with an inverse dynamics method from real captured work tasks. The chosen tasks were meat cutting tasks, well known to be highly correlated to musculoskeletal troubles appearance in the slaughter industry.

The experimental protocol consisted in recording three main data during meat cutting tasks, and analysing their variation when some of the workstation design parameters were changing.

Then the motion was replayed in the AnyBody modeling system (AnyBody, Aalborg, Denmark) in order to obtain muscle forces generated during the motion. A trend comparison has been done, comparing recorded and computed muscle activations. Results showed that most of the computed activations were qualitatively close from the recorded ones (similar shapes and peaks), but quantitative comparison leaded to major differences between recorded and computed activations (the trend followed by the recorded activations in regard of a workstation design parameter, such as the table height, is not obtained with the computed activations) [15] . We currently explore those results to see if the fact that co-contraction of single joints muscles is badly estimated by classical inverse dynamics method can be a reason of this issue. We also work on the co-contration simulation in order to improve the results.

This work has been done in collaboration with the Center for Sensory-motor Interaction (SMI, Aalborg University, Aalborg, Denmark), particularly Mark de Zee (Associate Professor) and Pascal Madeleine (Professor).

Furthermore, the fidelity of the VR simulator has to be evaluated. For example, a simulator for assembly task has been evaluated in comparing different types of interaction : real, virtual and virtual + force feedback. Objective and subjective metrics of discomfort led to highlight the influence of the environment on motor control and sensory feedback, changing more or less deeply the way the task is performed. The results particularly showed a distorsion between the user's subjective rating of discomfort and the objective value associated to the postures they reached during the task execution. Nevertheless, scores obtained in real and virtual environments for objective and subjective indicators of discomfort were highly correlated [17] , [16] . It indicates that despite the differences, the gap between real and virtual environments can be fullfiled. This work has been done within the frame of the european project FP7 VISIONAIR.

At last we proposed in collaboration with Thierry Duval (Hybrid team, Rennes) a new architecture for information sharing and bridging in collaborative virtual environements in application to ergonomics studies. This work has been awarded with a best paper award at The 4th IEEE conference on Cognitive Infocommunications (CogInfoCom 2013) [28] .