Inverse Dynamic Reconstruction of Truck Cabin Ingress/Egress Motions 2009-01-2286

This paper investigates the feasibility of calculating joint forces and moments during a whole body truck cabin ingress/egress motion. For such a task, it is difficult to evaluate a future truck instep as the influences of the architecture parameters are complex over the motion and the discomfort feeling. In order to evaluate the future product at an early stage of the design process, Digital Human Models (DHMs) are interesting tools. However, most existing DHM simulation packages can only efficiently evaluate the kinematics of postures where the dynamics of the whole motion is necessary for such a task. The enhancement of DHMs towards a dynamic analysis and modeling is therefore necessary.

In this study, the motions of subjects entering and exiting an adjustable truck cabin were measured by mean of an opto-electronic motion capture system and six load sensors. The joint angles were then calculated using an inverse kinematics method. And the joint loads were calculated using a classical Newton-Euler inverse dynamics method during the period when all the contact loads are measured. The comparison of the joint torques and forces at the spine L5/S1 joint calculated from the going up and going down methods show a good consistency and validate the moments and forces calculated at the other joints. In order to evaluate the joint loads when a sensor is missing, two methods are also presented, the first one making no assumption on the missing contact force, and the second one assuming that the center of pressure is known. The results show that more consistent joint loads were obtained using the method with assumption.

These results validate the dynamic motion reconstruction method and open the way for a discomfort evaluation of truck cabin ingress/egress based on joint moments and forces.