Multilayered Kinodynamics Simulation for Detailed Whole-Body Motion Generation and Analysis

Abstract

This study generates and analyzes unsafe human motions that cannot be measured experimentally in laboratories with dynamic consistency. Detailed whole-body motions are generated by a multilayered kinodynamics simulation (MLKD Sim) that uses a detailed digital whole-body human model and a simple motion-representation model that parametrically represents human motion mechanisms. First, we develop the simple motion-representation model that represents human motion and contact force data that are experimentally measured in a laboratory, and we identify this model's parameters based on these experimental data. Forward dynamics computation of this motion-representation model with changing model and/or environmental parameters simulates motion modification as well as a contact force with dynamic consistency. Finally, the mapping function from the motion-representation model's motion to the detailed motion identified from the experimental data is used to reconstruct the detailed whole-body motion. MLKD Sim reconstructs a vertical contact force with average error of 2.18E+02 N, center of mass trajectory with average error of 3.31E-02 m, ankle joint angle with average error of 1.11E-01 rad (2.95E+00%), and ankle joint torque with average error of 6.13E+01 Nm (1.93E+01%). Unsafe motion simulation results show that the physical load on the hip, knee, and ankle joints increases by 9.23E+01%, 5.42E+02%, and 1.45E+02% respectively with 0.5-m level difference in a running surface. These results imply that when sprinting in an unknown environment, we need to protect, in order, the knee ankle, and hip joints. This study conducts detailed dynamics and kinematics analysis of unsafe human motions that cannot be measured experimentally in laboratories to prevent injuries, falls, and fatigue, and these results should find applications in the fields of medicine and welfare.