Dynamic Roll-and-Rise Motion by an Adult-Size Humanoid Robot

Whole-body dynamic actions under various contacts with the environment will be very important for future humanoid robots to support human tasks in unstructured environments. Such skills are very difficult to realize using the standard motion control methodology based on asymptotic convergence to the successive desired states. An alternative approach would be to exploit the passive dynamics of the body under constrained motion, and to navigate through multiple dynamics by imposing the least control in order to robustly reach the goal state. As a first example of such a strategy, we propose and investigate a "Roll-and-Rise" motion. This is a fully dynamic whole-body task including underactuated motion whose state trajectory is insoluble, and unpredictable perturbations due to complex contacts with the ground. First, we analyze the global structure of Roll-and-Rise motion. Then the critical points are analyzed using simplified models and simulations. The results suggest a non-uniform control strategy which focuses on sparse critical points in the global phase space, and allows deviations and trade-offs at other parts. Finally, experiments with a real adult-size humanoid robot are successfully carried out. The robot rose from a flat-lying posture to a crouching posture within 2 seconds.