Active Variable-Impedance based Compliant Landing Control for a Hydraulically-Actuated Articulated Robotic Leg

Inspired from the time-variable impedance characteristics of human leg during locomotion, we designed an efficient compliant landing controller based on active variable-impedance and compliant-landing trajectory planning for a hydraulically-actuated and fully torque controlled robotic leg. The variable-impedance based compliant landing is enabled by a high-performance joint torque controller and a finite state machine consisting of swing, landing and supporting phases to synchronize different phases of the control process. With this approach, two experiments are implemented to evaluate the influence of landing phase duration on compliant landing behavior and the efficiency of our active variable-impedance controller. The experimental results demonstrate that the introduction of landing phase and active variable-impedance greatly improved the leg’s capability to absorb ground reaction force (GRF) peaks at touchdown. The ground reaction force peak of the leg during landing are reduced to a relatively low level which resemble the impact forces suffered by animals during locomotion as 180%-240% ofbody weight.