Joint impedance control applied to a biped pneumatic leg

Some fundamental properties must be verified when dealing with control of legged robots. Actually, to make the supervisor efficient, the control of each leg has to be highly reliable. Accuracy, robustness and rapidity are then required to ensure the stability of the platform and the tracking of dynamic gaits. To verify these three properties, we propose a general control architecture designed for a pneumatic biped robot and develop especially the limb level. This level is devoted to the control of each limb according to the desired position and force trajectories given by a coordinator level. The chosen trajectories are coming from biomechanical results and a dynamic model taking into account mechanic and pneumatic effects is presented. We propose to deal with the setting and the raising phases using a continuous joint impedance controller. The control design is based on a computed torque method taking into account the actuator and the mechanical models. The asymptotic stability is ensured using Popov criteria. Simulation results of this new controller are presented, leading to a good behaviour of the leg during the two phases at relatively high velocities