Modal-space control for articulated characters

We present a novel control algorithm for simulating an articulated character performing a given reference motion and its variations. The unique feature of our controller is its ability to make a long-horizon plan at every time step. Our algorithm overcomes the computational hurdle by applying modal analysis on a time-varying linear dynamic system. We exploit the properties of modal coordinates in two ways. First, we design separate control strategies for dynamically decoupled modes. Second, our controller only applies long-horizon planning on a subset of modes, largely reducing the size of the control problem. With this decoupled and reduced control system, the character is able to execute the reference motion while reacting to unexpected perturbations and anticipating changes in the environment. We demonstrate our results by simulating a variety of reference motions, such as walking, squatting, jumping, and swinging.