Estimation of Mass and Inertia Properties of Human Body Segments for Physics-based Human Modeling and Simulation Applications

This paper describes an effective integrated method for estimation of subject-specific mass, inertia tensor, and center of mass of individual body segments of a digital avatar for use with physics-based digital human modeling simulation environment. One of the main goals of digital human modeling and simulation environments is that a user should be able to change the avatar (from male to female to a child) at any given time. The user should also be able to change the various link dimensions, like lengths of upper and lower arms, lengths of upper and lower legs, etc. These customizations in digital avatar's geometry change the kinematic and dynamic properties of various segments of its body. Hence, the mass and center of mass/inertia data of the segments must be updated before simulating physics-based realistic motions. Most of the current methods use mass and inertia properties calculated from a set of regression equations based on average of some population. In this paper, we calculate avatar-specific mass and inertia properties from the scans of digital human. The mesh of the digital human model is split using equations defined by a plane at each joint. The equation is used to split up the geometry. The resultant geometry is closed to make the mesh hole free. Mass, center of mass (assuming uniform density) and inertia tensor are then calculated using the method described in the paper (Mirtich 1996). The method can be used in all physics-based digital human modeling and simulation software where the scan of the avatar is available. The use of mass inertia properties calculated by this method enables users to customize digital avatar and simulate motions for specifically for that avatar.