Development of a compliance controller to reduce energy consumption for bipedal robots

• Published in: Autonomous robots Vol. 24; no. 4; pp. 419 - 434
• Main Authors: Vanderborght, Bram, Verrelst, Björn, Van Ham, Ronald, Van Damme, Michaël, Beyl, Pieter, Lefeber, Dirk
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.05.2008; Springer Nature B.V
• Subjects: Actuators; Artificial Intelligence; Artificial muscles; Compliance; Computer Imaging; Control; Controllers; Energy consumption; Engineering; Joints (anatomy); Mechatronics; Pattern Recognition and Graphics; Pendulums; Physical properties; Robotics; Robotics and Automation; Robots; Stability; Stiffness; Strategy; Studies; Tracking control; Trajectory control; Vision; Walking; Energy-efficient walking; Torque and compliance control; Biped; Pneumatic artificial muscle
• ISSN: 0929-5593; 1573-7527
• DOI: 10.1007/s10514-008-9088-5

In this paper a strategy is proposed to combine active trajectory tracking for bipedal robots with exploiting the natural dynamics by simultaneously controlling the torque and stiffness of a compliant actuator. The goal of this research is to preserve the versatility of actively controlled humanoids, while reducing their energy consumption. The biped Lucy, powered by pleated pneumatic artificial muscles, has been built and controlled and is able to walk up to a speed of 0.15 m/s. The pressures inside the muscles are controlled by a joint trajectory tracking controller to track the desired joint trajectories calculated by a trajectory generator. However, the actuators are set to a fixed stiffness value. In this paper a compliance controller is presented to reduce the energy consumption by controlling the stiffness. A mathematical formulation has been developed to find an optimal stiffness setting depending on the desired trajectory and physical properties of the system and the proposed strategy has been validated on a pendulum structure powered by artificial muscles. This strategy has not been implemented on the real robot because the walking speed of the robot is currently too slow to benefit already from compliance control.