Modeling and Hybrid Compliant Control for a 2-DOF Robotic Leg With a New Biarticular Actuation

It is well-known that, biarticular muscles are those that cross two joints rather than one to generate high torque at both joints. Such muscles play an essential role in human locomotion since they provide large forces. Different mono- and bi-articular actuations for a two- or three-link robotic leg have been developed in literature to study the human locomotion. In this paper, a new bio-inspired biarticular actuation configuration with mono articular rotary actuation for the proximal link and biarticular linear actuation for the distal link is proposed for a two-link robotic leg. Since the spring loaded inverted pendulum (SLIP) simplifies the human locomotion, the new proposed configuration is developed to realize the SLIP behavior during ground interaction and to show robustness against any impact from the environment. Full kinematic and dynamic analyses for the new configuration are developed in the biarticular coordinates. The derived dynamic model is then mapped to a rotating task space which best represents the swing and stance phases of the human gait. Thereafter, a unified framework for a hybrid impedance and position controller is developed in the rotating task space; while the controller gains are optimized to reduce the tracking errors and reject any disturbance. Simulation results prove the effectiveness of the proposed approach.