Torque-control based compliant actuation of a quadruped robot

In the realm of legged locomotion, being compliant to external unperceived impacts is crucial when negotiating unstructured terrain. Impedance control is a useful framework to allow the robot to follow reference trajectories and, at the same time, handle external disturbances. To implement impedance control, high performance torque control in all joints is of great importance. In this paper, the torque control for the electric joints of the HyQ robot is described and its performance assessed. HyQ is a quadruped robot which has hybrid actuation: hydraulic and electric. This work complements our previous work, in which the torque control for the hydraulic joints was addressed. Subsequently, we describe the implementation of an impedance controller for the HyQ leg. Experimental results assess the tracking capability of a desired Cartesian force at the end-effector under the action of external disturbances. Another set of experiments involves the tracking and the shaping of different desired stiffness behaviors (stiffness ellipses) at the foot.