Locomotion Control Architecture for the Pneumatic Biped Lucy consisting of a Trajectory Generator and Joint Trajectory Tracking Controller

The biped Lucy is actuated with pleated pneumatic artificial muscles because compliant actuation is important for energy-efficient legged locomotion. To control such a robot a specific control architecture is needed. In this paper we propose a trajectory generator and a joint trajectory tracking controller. The first one calculates dynamic balanced trajectories and is based on an inverted pendulum approximation, which models the robot as a single point mass. The trajectory generator allows the step-length, intermediate foot lift and velocity to be chosen for each step while keeping the zero moment point (ZMP) in the ankle point during the single support phase and it provides a smooth transition of the ZMP from the rear ankle point to the front ankle point during the double support phase. This strategy can be used for every biped. The second part is very specific for a robot powered with pneumatic artificial muscles. Out of the desired trajectories the pressures inside the muscles are calculated. The proposed combination is successfully implemented and the robot is able to walk at 0.11 m/s