Active compliance hybrid zero dynamics control of bounding on HyQ

This paper presents a control law that induces stable bounding on a model of the quadrupedal robot HyQ designed specifically for highly-dynamic locomotion. The controller integrates active compliance and torque planning with the framework of hybrid zero dynamics. Exploiting the hybrid nature of the system, the control action is developed in both continuous and discrete time to regulate the torque applied at the support leg and the motion of the swing leg. It is demonstrated that the proposed control law is capable of producing stable periodic bounding gaits. The controller is tested in simulations under different perturbations, including an unexpected vertical disturbance in ground height that amounts to 15% of the leg length, as well as under parameter uncertainty.