On dynamic control of pneumatic bipeds

Abstract

Some fundamental properties must be verified when dealing with the dynamic control of legged robots. Actually, to make the robot follow a given gait, the control strategy has to ensure dynamic stability in real time. Moreover, to make the supervisor efficient, the control of each leg has lo be highly reliable. Accuracy robustness, and rapidly are then required to follow dynamic motions. To verify these properties, we propose a general control architecture designed for pneumatic legged robots and develop it for a biped. This control architecture is composed of two main levels. The upper one, called the “Coordinator” level, maintains the robot stability by correcting on line its center of mass acceleration and distributing correctly the forces on each limb. The lower level, called the “Limb” level, is devoted to the control of each limb according to the desired position and force trajectories given by the Coordinator level. The chosen trajectories are derived from biomechanical results, and a dynamic model that takes into account mechanical and pneumatic effects is presented. We propose to deal with the setting and the raising phases, using a continuous nonlinear joint impedance controller. The asymptotic stability is ensured by using Popov criteria. Simulation results of this new controller are presented, leading to a good behavior of the leg during the two phases at relatively high velocities. © 1998 John Wiley & Sons, Inc.