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A method to simulate digital human running using an optimization-based approach is presented. The digital human is considered as a mechanical system that includes link lengths, mass moments of inertia, joint torques, and external forces. The problem is formulated as an optimization problem to determine the joint angle profiles. The kinematics analysis of the model is carried out using the Denavit-Hartenberg method. The B-spline approximation is used for discretization of the joint angle profiles, and the recursive formulation is used for the dynamic equilibrium analysis. The equations of motion thus obtained are treated as equality constraints in the optimization process. With this formulation, a method for the integration of constrained equations of motion is not required. This is a unique feature of the present formulation and has advantages for the numerical solution process.

This paper presents a validation study of a physics-based simulation of human walking. We simulated four different subjects walking on the level with nine different backpacks. Compared against experimental data of subjects under the same conditions, simulation results are shown to predict peak ground reaction forces, joint angles, and the subjects’ adjustment to lean angle necessary to dynamically balance the load and achieve stable walking at 1.4 m/s.

Boston Dynamics is developing the Digital Biomechanics Laboratory (DBL), a physics-based modeling tool for simulating humans and equipment. A key distinction of the DBL is the ability to simulate actively controlled human behavior, tasks such as walking, running, and carrying loads. The DBL combines forward dynamics simulation of the body, contact detection, contact force modeling, equipment modeling, and advanced control to simulate realistic human tasks. We are using the DBL to study the biomechanics of load carriage. In this paper we report on our effort to validate the simulation through comparisons to live subject experiments.