Synthesizing physically realistic human motion in low-dimensional, behavior-specific spaces
ACM SIGGRAPH 2004 Papers
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The 3D simulation of human activity based on physics, kinematics, and dynamics in terrestrial and space environments, is becoming increasingly important in robotics, computer graphics, biomechanics, and virtual reality. Virtual humans may be used to design tasks in terrestrial environments and analyze their physical workload to maximize success and safety without expensive physical mockups (e.g. partially realistic neutral-buoyancy tanks for space activity analyzing). In our previous paper {Lo3}, we presented an efficient optimal control and recursive dynamics based animation system for simulating and controlling the motion of articulated figures, and implemented the approach to several experiments where the simplified articulated models which has a serial/closed-loop chain structures with only small degree-of-freedom (less than seven) each. The computation time is from a few minutes up to 4 hours based on the complexity of the model and how close is the initial guess of the motion trajectory to the optimal solution. This paper presents an improved method, which can deal with more complicated kinematic chains --tree-structures -- as well as larger degree-of-freedom serial/closed-loop chain structures. Motion planning is done by first solving the inverse kinematic problem to generate possible trajectories, which gives us a better initial guess of the motion trajectory than the previous one, and then by solving the resulting nonlinear optimal control problem. For example, minimization of the torques during a simulation under certain constraints is often applied and has its origin in the biomechanics literature. Examples of activities shown are chinup and dipdown in different terrestrial environments as well as zero gravity self-orientation and ladder traversal.