GRASP Special Seminar - Koushil Sreenath, University of Michigan, "Achieving Walking and Running on a Biped with Compliance: A Feedback Control Design"

Abstract: MABEL is a planar bipedal test bed with no feet, weighs around 65 Kg, is 1 m tall at the hips, and has a novel transmission with a series compliant element to enhance energy efficiency and agility of dynamic locomotion. The presence of compliance in MABEL’s transmission has led to new control challenges: Compliance increases the degree of underactuation, and also raises the question of how to use the compliance effectively.

This talk will illustrate a controller design based on the Hybrid Zero Dynamics (HZD) that preserves the natural compliant dynamics of the system to achieve provably stable, efficient, fast and robust bipedal walking resulting in a walking gait with mechanical cost of transport that is just a factor of two away from that of humans, and in a walking world speed record of 1.5 m/s.

Further, biomechanics studies have shown that humans and animals adjust their leg stiffness to accommodate for variations in terrain and ground stiffness during running using a combination of tendons, and muscles. Motivated by this, a novel control design that embeds an active force control in the form of virtual compliance within the compliant HZD framework will be presented to achieve running gaits on MABEL.