Sensitivity Analysis of Performance on Reach Tasks considering Joint Angle and Link Length Variability
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Due to variability in human anthropometry, no two people will perform a task in exactly the same way—different people will adapt different postures to perform the same reach task, and even for the same person and reach task, postures will vary with time. In design using digital human modeling problems, it is important to consider anthropometric uncertainty when the resulting product, such as a vehicle interior, may affect the comfort of the user. Currently, techniques in digital human modeling applications primarily employ deterministic methods which do not properly account for variability. An alternative to deterministic methods is probabilistic/sensitivity analysis. This study presents a sensitivity approach to gain insights into how uncertainty affects performance on general reach tasks and reach tasks within a vehicle. Sensitivity levels are found to determine the importance of each joint angle and link length to the final reach. Three digital human upper body models with 21 degrees of freedom (DOF), 30 DOF, and 55 DOF are introduced to demonstrate the sensitivity approach for reach tasks using one arm, both arms, and the full body, respectively. Seven reach points within a vehicle and eighteen general reach tasks are used to compare the sensitivities due to joint angle and link length uncertainty. The results show that the importance of each joint angle or link length is dependent on the nature of the reach task; sensitivities for joint angles and link lengths are different for each reach task.