A pneumatic biped: experimental walking results and compliance adaptation experiments

This paper reports on the control structure of the pneumatic biped Lucy. The robot is actuated with pleated pneumatic artificial muscles, which have interesting characteristics that can be exploited for legged locomotion. They have a high power to weight ratio, an adaptable compliance and they can absorb impact effects. In a first part of this paper a discussion on the control architecture, which focuses on the joint trajectory generator and the joint trajectory tracking controller, is given. The trajectory generator calculates trajectories represented by polynomials based on objective locomotion parameters, which are average forward speed, step length, step height and intermediate foot lift. The joint trajectory tracking controller is divided in three parts: a computed torque module, a delta-p unit and a bang-bang pressure controller. The first results of the incorporation of this control architecture in the real biped Lucy are given. Several essential graphs showing tracking performance and pressure regulation are given and the effectiveness of the control algorithm is discussed. A second part of the paper focusses on compliance adaptation which is used for exploitation of the natural dynamics with respect to different walking patterns. A mathematical formulation for this purpose is explained. The compliance adaptation strategy is not yet implemented for the robot Lucy, but some experimental results are given for a one DOF pendulum structure. These clearly show the effectiveness and importance of the adaptation strategy